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Second Sino-Japanese War
Part of the interwar period and the Pacific War
Clockwise: Japanese landing forces in gas masks during the Battle of Shanghai NRA forces on the Great Wall Nanjing Massacre victims on the Qinhuai River shore Chinese machine gun nest at the Battle of Wuhan Japanese Mitsubishi Ki-21 in the bombing of Chongqing Chinese Expeditionary Force marching in India
Date 7 July 1937 – 2 September 1945 (8 years, 1 month, 3 weeks and 5 days) Location Mainland China Indochina Burma Result Chinese victory Territorial changes China recovers territories lost to Japan since the Treaty of Shimonoseki
Belligerents
China Kuomintang Chinese Communist Party	Japan Manchukuo Mengjiang  Wang Jingwei regime
Commanders and leaders
Chiang Kai-shek Mao Zedong He Yingqin Chen Cheng Cheng Qian Bai Chongxi Xu Yongchang Li Zongren	Hirohito Hideki Tojo Shunroku Hata Yasuji Okamura Prince Kotohito # Otozō Yamada Hajime Sugiyama
Strength
14 million total Nationalists 1.7 million (1937) 2.6 million (1939) 5.7 million (1945) Communists 640,000 (1937) 166,700 (1938) 488,744 (1940) 1.2 million (1945)	4.1 million total Japan 600,000 (1937) 1,015,000 (1939) 1,124,900 Puppet states 900,000–1,006,086 (1945)
Casualties and losses
Official Nationalist data 1,319,958 killed 1,761,335 wounded 130,116 missing 3,211,409 total Year-by-year loss statistic Combat losses : 1,319,358 killed 1,759,715 wounded 116,593 missing 3,195,666 total Other losses : 10,322,934 Postwar investigations National Revolutionary Army: Army : 1,357,222 killed 1,735,969 wounded 298,233 missing 3,391,424 total Air Force : 721 officers and 11,028 NCOs and privates killed 842 officers and 1,446 NCOs and privates wounded 14,037 total Navy : 403 officers and 2,000 NCOs and privates killed 67 officers wounded 2,470 total Whole armed forces : 1,371,374 killed 1,738,324 wounded 298,233 missing 3,407,931 total Air Defense Service : 1,042 killed 1,271 wounded 2,313 total Other losses Losses of wounded and sick in hospitals directly administered by the Nationalist Government : Wounded soldiers : 45,710 dead 123,017 crippled 274,671 deserted 443,398 total Sick soldiers : 422,479 dead 191,644 crippled 323,436 deserted 937,559 total Total : 468,189 dead 314,661 crippled 598,107 deserted 1,380,957 total Estimated number of deserters in the war : 5.894-5.971 million Other Nationalist estimates 3–4 million+ dead and missing 500,000 captured 3.2–10 million+ total Official Communist data 160,603 dead 290,467 wounded 87,208 missing 45,989 POWs 584,267 total Other Communist estimates 446,740 total Total 3.8–10.6 million+ casualties 1 million+ captured 266,800–1,000,000 POWs dead	Japanese medical data 455,700–700,000 military dead (excluding Northeast China and Burma) According to the Ministry of Health, Labour, and Welfare in 1977 In China (excluding Northeast China) : 465,700 deaths (including 23,500 at sea) In Northeast China : 245,400 deaths Number of POWs according to Yasuji Okamura's diary in May 1946 Repatriated by the Nationalists  : 1,212 army personnel 40 navy personnel 106 merchants and civilians Repatriated by the Communists : about 300 POWs Deaths in Kuomintang POW camps : more than 200 POWs Total : at least 1,858 captured According to He Yingqin 1,934,820 wounded and missing 22,293+ captured 2.5 million+ total casualties Puppet state forces 288,140–574,560 dead 742,000 wounded Middle estimate: 960,000 dead and wounded Total 3.0–3.6 million casualties
15–22 million total casualties
^ After July 1937; excluding Manchuria and Burma Deaths from illness, dismissals, and desertions Including losses : In guerilla fighting In the Mukden Incident, January 28 Incident, and Defense of the Great Wall This number does not include Japanese killed by Chinese forces in the Burma campaign and does not include Japanese killed in Manchuria. Including deaths after the war ^ Excluding more than 1 million who were disarmed following the surrender of Japan Including casualties of Japanese puppet forces. The combined toll is most likely around 3,500,000: 2.5 million Japanese, per their own records, and 1 million collaborators.

The Second Sino-Japanese War was fought between the Republic of China and the Empire of Japan between 1937 and 1945, following a period of war localized to Manchuria that started in 1931. It is considered part of World War II, and often regarded as the beginning of World War II in Asia. It was the largest Asian war in the 20th century and has been described as "the Asian Holocaust", in reference to the scale of Japanese war crimes against Chinese civilians. It is known in China as the War of Resistance against Japanese Aggression (simplified Chinese: 抗日战争; traditional Chinese: 抗日戰爭).

On 18 September 1931, the Japanese staged the Mukden incident, a false flag event fabricated to justify their invasion of Manchuria and establishment of the puppet state of Manchukuo. This is sometimes marked as the beginning of the war. From 1931 to 1937, China and Japan engaged in skirmishes, including in Shanghai and in Northern China. Chinese Nationalist and Communist forces, respectively led by Chiang Kai-shek and Mao Zedong, had fought each other in the Chinese Civil War since 1927. In late 1933, Chiang Kai-shek encircled the Chinese Communists in an attempt to finally destroy them, forcing the Communists into the Long March, resulting in the Communists losing around 90% of their men. As a Japanese invasion became imminent, Chiang still refused to form a united front before he was placed under house arrest by his subordinates who forced him to form the Second United Front in late 1936 in order to resist the Japanese invasion together.

The full-scale war began on 7 July 1937 with the Marco Polo Bridge incident near Beijing, which prompted a full-scale Japanese invasion of the rest of China. The Japanese captured the capital of Nanjing in 1937 and perpetrated the Nanjing Massacre. After failing to stop the Japanese capture of Wuhan in 1938, then China's de facto capital at the time, the Nationalist government relocated to Chongqing in the Chinese interior. After the Sino-Soviet Non-Aggression Pact, Soviet aid bolstered the National Revolutionary Army and Air Force. By 1939, after Chinese victories at Changsha and with Japan's lines of communications stretched deep into the interior, the war reached a stalemate. The Japanese were unable to defeat Chinese Communist Party forces in Shaanxi, who waged a campaign of sabotage and guerrilla warfare. In November 1939, Chinese nationalist forces launched a large scale winter offensive, and in August 1940, communist forces launched the Hundred Regiments Offensive in central China.

In December 1941, Japan launched a surprise attack on Pearl Harbor and declared war on the United States. The US increased its aid to China under the Lend-Lease Act, becoming its main financial and military supporter. With Burma cut off, the United States Army Air Forces airlifted material over the Himalayas. In 1944, Japan launched Operation Ichi-Go, the invasion of Henan and Changsha. In 1945, the Chinese Expeditionary Force resumed its advance in Burma and completed the Ledo Road linking India to China. China launched large counteroffensives in South China and repulsed a failed Japanese invasion of West Hunan and recaptured Japanese occupied regions of Guangxi.

Japan formally surrendered on 2 September 1945, following the atomic bombings of Hiroshima and Nagasaki, Soviet declaration of war and subsequent invasions of Manchukuo and Korea. The war resulted in the deaths of around 20 million people, mostly Chinese civilians. China was recognized as one of the Four Policemen, regained all territories lost, and became one of the five permanent members of the United Nations Security Council. The Chinese Civil War resumed in 1946, ending with a communist victory and the Proclamation of the People's Republic of China in 1949.

Names

In China, the war is most commonly known as the "War of Resistance against Japanese Aggression" (simplified Chinese: 抗日战争; traditional Chinese: 抗日戰爭), and shortened to "Resistance against Japanese Aggression" (抗日) or the "War of Resistance" (抗战; 抗戰). It was also called the "Eight Years' War of Resistance" (八年抗战; 八年抗戰), but in 2017 the Chinese Ministry of Education issued a directive stating that textbooks were to refer to the war as the "Fourteen Years' War of Resistance" (十四年抗战; 十四年抗戰), reflecting a focus on the broader conflict with Japan going back to the 1931 Japanese invasion of Manchuria. According to historian Rana Mitter, historians in China are unhappy with the blanket revision, and (despite sustained tensions) the Republic of China did not consider itself to be in an ongoing war with Japan over these six years. It is also referred to as part of the "Global Anti-Fascist War".

In contemporary Japan, the name "Japan–China War" (Japanese: 日中戦争, romanized: Nitchū Sensō) is most commonly used because of its perceived objectivity. When the invasion of China proper began in earnest in July 1937 near Beijing, the government of Japan used "The North China Incident" (北支事變/華北事變, Hokushi Jihen/Kahoku Jihen), and with the outbreak of the Battle of Shanghai the following month, it was changed to "The China Incident" (支那事變, Shina Jihen).

The word "incident" (事變, jihen) was used by Japan, as neither country had made a formal declaration of war. From the Japanese perspective, localizing these conflicts was beneficial in preventing intervention from other countries, particularly the United Kingdom and the United States, which were its primary source of petroleum and steel respectively. A formal expression of these conflicts would potentially lead to an American embargo in accordance with the Neutrality Acts of the 1930s. In addition, due to China's fractured political status, Japan often claimed that China was no longer a recognizable political entity on which war could be declared.

Other names

In Japanese propaganda, the invasion of China became a crusade (聖戦, seisen), the first step of the "eight corners of the world under one roof" slogan (八紘一宇, Hakkō ichiu). In 1940, Japanese prime minister Fumimaro Konoe launched the Taisei Yokusankai. When both sides formally declared war in December 1941, the name was replaced by "Greater East Asia War" (大東亞戰爭, Daitōa Sensō).

Although the Japanese government still uses the term "China Incident" in formal documents, the word Shina is considered derogatory by China and therefore the media in Japan often paraphrase with other expressions like "The Japan–China Incident" (日華事變／日支事變, Nikka Jiken/Nisshi Jiken), which were used by media as early as the 1930s.

The name "Second Sino-Japanese War" is not commonly used in Japan as the China it fought a war against in 1894 to 1895 was led by the Qing dynasty, and thus is called the Qing-Japanese War (日清戦争, Nisshin–Sensō), rather than the First Sino-Japanese War.

Another term for the second war between Japan and China is the "Japanese invasion of China", a term used mainly in foreign and Chinese narratives.

Background

The origins of the Second Sino-Japanese War can be traced to the First Sino-Japanese War (1894–1895), in which China, then under the rule of the Qing dynasty, was defeated by Japan and forced to cede Taiwan and recognize the full and complete independence of Korea in the Treaty of Shimonoseki. Japan also annexed the Senkaku Islands, which Japan claims were uninhabited, in early 1895 as a result of its victory at the end of the war. Japan had also attempted to annex the Liaodong Peninsula following the war, though was forced to return it to China following the Triple Intervention by France, Germany, and Russia. The Qing dynasty was on the brink of collapse due to internal revolts and the imposition of the unequal treaties, while Japan had emerged as a great power through its efforts to modernize. In 1905, Japan successfully defeated the Russian Empire in the Russo-Japanese War, gaining Dalian and southern Sakhalin and establishing a protectorate over Korea.

Warlords in the Republic of China

In 1911, factions of the Qing Army uprose against the government, staging a revolution that swept across China's southern provinces. The Qing responded by appointing Yuan Shikai, commander of the loyalist Beiyang Army, as temporary prime minister in order to subdue the revolution. Yuan, wanting to remain in power, compromised with the revolutionaries, and agreed to abolish the monarchy and establish a new republican government, under the condition he be appointed president of China. The new Beiyang government of China was proclaimed in March 1912, after which Yuan Shikai began to amass power for himself. In 1913, the parliamentary political leader Song Jiaoren was assassinated; it is generally believed Yuan Shikai ordered the assassination. Yuan Shikai then forced the parliament to pass a bill to strengthen the power of the president and sought to restore the imperial system, becoming the new emperor of China.

However, there was little support for an imperial restoration among the general population, and protests and demonstrations soon broke out across the country. Yuan's attempts at restoring the monarchy triggered the National Protection War, and Yuan Shikai was overthrown after only a few months. In the aftermath of Shikai's death in June 1916, control of China fell into the hands of the Beiyang Army leadership. The Beiyang government was a civilian government in name, but in practice it was a military dictatorship with a different warlord controlling each province of the country. China was reduced to a fractured state. As a result, China's prosperity began to wither and its economy declined. This instability presented an opportunity for nationalistic politicians in Japan to press for territorial expansion.

Twenty-One Demands

In 1915, Japan issued the Twenty-One Demands to extort further political and commercial privilege from China, which was accepted by the regime of Yuan Shikai. Following World War I, Japan acquired the German Empire's sphere of influence in Shandong province, leading to nationwide anti-Japanese protests and mass demonstrations in China. The country remained fragmented under the Beiyang Government and was unable to resist foreign incursions. For the purpose of unifying China and defeating the regional warlords, the Kuomintang (KMT) in Guangzhou launched the Northern Expedition from 1926 to 1928 with limited assistance from the Soviet Union.

Jinan incident

The National Revolutionary Army (NRA) formed by the Kuomintang swept through southern and central China until it was checked in Shandong, where confrontations with the Japanese garrison escalated into armed conflict. The conflicts were collectively known as the Jinan incident of 1928, during which time the Japanese military killed several Chinese officials and fired artillery shells into Jinan. According to the investigation results of the Association of the Families of the Victims of the Jinan massacre, it showed that 6,123 Chinese civilians were killed and 1,701 injured. Relations between the Chinese Nationalist government and Japan severely worsened as a result of the Jinan incident.

Reunification of China (1928)

As the National Revolutionary Army approached Beijing, Zhang Zuolin decided to retreat back to Manchuria, before he was assassinated by the Kwantung Army in 1928. His son, Zhang Xueliang, took over as the leader of the Fengtian clique in Manchuria. Later in the same year, Zhang declared his allegiance to the Nationalist government in Nanjing under Chiang Kai-shek, and consequently, China was nominally reunified under one government.

1929 Sino-Soviet war

The July–November 1929 conflict over the Chinese Eastern Railroad (CER) further increased the tensions in the Northeast that led to the Mukden Incident and eventually the Second Sino-Japanese War. The Soviet Red Army victory over Xueliang's forces not only reasserted Soviet control over the CER in Manchuria but revealed Chinese military weaknesses that Japanese Kwantung Army officers were quick to note.

The Soviet Red Army performance also stunned the Japanese. Manchuria was central to Japan's East Asia policy. Both the 1921 and 1927 Imperial Eastern Region Conferences reconfirmed Japan's commitment to be the dominant power in the Northeast. The 1929 Red Army victory shook that policy to the core and reopened the Manchurian problem. By 1930, the Kwantung Army realized they faced a Red Army that was only growing stronger. The time to act was drawing near and Japanese plans to conquer the Northeast were accelerated.

Chinese Communist Party

In 1930, the Central Plains War broke out across China, involving regional commanders who had fought in alliance with the Kuomintang during the Northern Expedition, and the Nanjing government under Chiang. The Chinese Communist Party (CCP) previously fought openly against the Nanjing government after the Shanghai massacre of 1927, and they continued to expand during this protracted civil war. The Kuomintang government in Nanjing decided to focus their efforts on suppressing the Chinese Communists through the Encirclement Campaigns, following the policy of "first internal pacification, then external resistance" (Chinese: 攘外必先安內).

After the defeat of the Chinese Soviet Republic by the Nationalists, the Communists retreated on the Long March to Yan'an. The Nationalist government ordered local warlords to continue the campaign against the Communists rather than focus on the Japanese threat. A December 1936 coup by two Nationalist Generals, the Xi'an Incident, forced Chiang Kai-shek to accept a United Front with the Communists to oppose Japan.

Invasion of Manchuria and Northern China

The internecine warfare in China provided excellent opportunities for Japan, which saw Manchuria as a limitless supply of raw materials, a market for its manufactured goods (now excluded from the markets of many Western countries as a result of Depression-era tariffs), and a protective buffer state against the Soviet Union in Siberia. As a result, the Japanese Army was widely prevalent in Manchuria immediately following the Japanese victory in the Russo-Japanese War in 1905, where Japan gained significant territory in Manchuria. As a result of their strengthened position, by 1915 Japan had negotiated a significant amount of economic privilege in the region by pressuring Yuan Shikai, the president of the Republic of China at the time. With a widened range of economic privileges in Manchuria, Japan began focusing on developing and protecting matters of economic interests. This included railroads, businesses, natural resources, and a general control of the territory. With its influence growing, the Japanese Army began to justify its presence by stating that it was simply protecting its own economic interests. However militarists in the Japanese Army began pushing for an expansion of influence, leading to the Japanese Army assassinating the warlord of Manchuria, Zhang Zuolin. This was done with hopes that it would start a crisis that would allow Japan to expand their power and influence in the region. When this was not as successful as they desired, Japan then decided to invade Manchuria outright after the Mukden incident in September 1931. Japanese soldiers set off a bomb on the Southern Manchurian Railroad in order to provoke an opportunity to act in "self defense" and invade outright. Japan charged that its rights in Manchuria, which had been established as a result of its victory in 1905 at the end of the Russo-Japanese War, had been systematically violated and there were "more than 120 cases of infringement of rights and interests, interference with business, boycott of Japanese goods, unreasonable taxation, detention of individuals, confiscation of properties, eviction, demand for cessation of business, assault and battery, and the oppression of Korean residents".

After five months of fighting, Japan established the puppet state of Manchukuo in 1932, and installed the last Emperor of China, Puyi, as its puppet ruler. Militarily too weak to challenge Japan directly, China appealed to the League of Nations for help. The League's investigation led to the publication of the Lytton Report, condemning Japan for its incursion into Manchuria, causing Japan to withdraw from the League of Nations. No country took action against Japan beyond tepid censure. From 1931 until summer 1937, the Nationalist Army under Chiang Kai-shek did little to oppose Japanese encroachment into China.

Incessant fighting followed the Mukden Incident. In 1932, Chinese and Japanese troops fought the 28 January battle. This resulted in the demilitarization of Shanghai, which forbade the Chinese to deploy troops in their own city. In Manchukuo there was an ongoing campaign to pacify the Anti-Japanese Volunteer Armies that arose from widespread outrage over the policy of non-resistance to Japan. On 15 April 1932, the Chinese Soviet Republic led by the Communists declared war on Japan.

In 1933, the Japanese attacked the Great Wall region. The Tanggu Truce established in its aftermath, gave Japan control of Rehe Province, as well as a demilitarized zone between the Great Wall and Beijing-Tianjin region. Japan aimed to create another buffer zone between Manchukuo and the Chinese Nationalist government in Nanjing.

Japan increasingly exploited China's internal conflicts to reduce the strength of its fractious opponents. Even years after the Northern Expedition, the political power of the Nationalist government was limited to just the area of the Yangtze River Delta. Other sections of China were essentially in the hands of local Chinese warlords. Japan sought various Chinese collaborators and helped them establish governments friendly to Japan. This policy was called the Specialization of North China (華北特殊化; huáběitèshūhùa), more commonly known as the North China Autonomous Movement. The northern provinces affected by this policy were Chahar, Suiyuan, Hebei, Shanxi, and Shandong.

This Japanese policy was most effective in the area of what is now Inner Mongolia and Hebei. In 1935, under Japanese pressure, China signed the He–Umezu Agreement, which forbade the KMT to conduct party operations in Hebei. In the same year, the Chin–Doihara Agreement was signed expelling the KMT from Chahar. Thus, by the end of 1935 the Chinese government had essentially abandoned northern China. In its place, the Japanese-backed East Hebei Autonomous Council and the Hebei–Chahar Political Council were established. There in the empty space of Chahar the Mongol military government was formed on 12 May 1936. Japan provided all the necessary military and economic aid. Afterwards Chinese volunteer forces continued to resist Japanese aggression in Manchuria, and Chahar and Suiyuan.

Some Chinese historians believe the 18 September 1931 Japanese invasion of Manchuria marks the start of the War of Resistance. Although not the conventional Western view, British historian Rana Mitter describes this Chinese trend of historical analysis as "perfectly reasonable". In 2017, the Chinese government officially announced that it would adopt this view. Under this interpretation, the 1931–1937 period is viewed as the "partial" war, while 1937–1945 is a period of "total" war. This view of a fourteen-year war has political significance because it provides more recognition for the role of northeast China in the War of Resistance.

1937: Full-scale invasion of China

On the night of 7 July 1937, Chinese and Japanese troops exchanged fire in the vicinity of the Marco Polo (or Lugou) Bridge about 16 km from Beijing. The initial confused and sporadic skirmishing soon escalated into a full-scale battle.

Unlike Japan, China was unprepared for total war and had little military-industrial strength, no mechanized divisions, and few armoured forces.

Within the first year of full-scale war, Japanese forces obtained victories in most major Chinese cities.

Battle of Beiping–Tianjin

On 11 July, in accordance with the Goso conference, the Imperial Japanese Army General Staff authorized the deployment of an infantry division from the Chōsen Army, two combined brigades from the Kwantung Army and an air regiment composed of 18 squadrons as reinforcements to Northern China. By 20 July, total Japanese military strength in the Beijing-Tianjin area exceeded 180,000 personnel.

The Japanese gave Sung and his troops "free passage" before moving in to pacify resistance in areas surrounding Beijing (then Beiping) and Tianjin. After 24 days of combat, the Chinese 29th Army was forced to withdraw. The Japanese captured Beijing and the Taku Forts at Tianjin on 29 and 30 July respectively, thus concluding the Beijing-Tianjin campaign. By August 1937, Japan had occupied Beijing and Tianjin.

However, the Japanese Army had been given orders not to advance further than the Yongding River. In a sudden volte-face, the Konoe government's foreign minister opened negotiations with Chiang Kai-shek's government in Nanjing and stated: "Japan wants Chinese cooperation, not Chinese land." Nevertheless, negotiations failed to move further. The Ōyama Incident on 9 August escalated the skirmishes and battles into full scale warfare.

The 29th Army's resistance (and poor equipment) inspired the 1937 "Sword March", which—with slightly reworked lyrics—became the National Revolutionary Army's standard marching cadence and popularized the racial epithet guizi to describe the Japanese invaders.

Battle of Shanghai

The Imperial General Headquarters (GHQ) in Tokyo, content with the gains acquired in northern China following the Marco Polo Bridge Incident, initially showed reluctance to escalate the conflict into a full-scale war. Following the shooting of two Japanese officers who were attempting to enter the Hongqiao military airport on 9 August 1937, the Japanese demanded that all Chinese forces withdraw from Shanghai; the Chinese outright refused to meet this demand. In response, both the Chinese and the Japanese marched reinforcements into the Shanghai area. Chiang concentrated his best troops north of Shanghai in an effort to impress the city's large foreign community and increase China's foreign support.

On 13 August 1937, Kuomintang soldiers attacked Japanese Marine positions in Shanghai, with Japanese army troops and marines in turn crossing into the city with naval gunfire support at Zhabei, leading to the Battle of Shanghai. On 14 August, Chinese forces under the command of Zhang Zhizhong were ordered to capture or destroy the Japanese strongholds in Shanghai, leading to bitter street fighting. In an attack on the Japanese cruiser Izumo, Kuomintang planes accidentally bombed the Shanghai International Settlement, which led to more than 3,000 civilian deaths.

In the three days from 14 to 16 August 1937, the Imperial Japanese Navy (IJN) sent many sorties of the then-advanced long-ranged G3M medium-heavy land-based bombers and assorted carrier-based aircraft with the expectation of destroying the Chinese Air Force. However, the Imperial Japanese Navy encountered unexpected resistance from the defending Chinese Curtiss Hawk II/Hawk III and P-26/281 Peashooter fighter squadrons; suffering heavy (50%) losses from the defending Chinese pilots (14 August was subsequently commemorated by the KMT as China's Air Force Day).

The skies of China had become a testing zone for advanced biplane and new-generation monoplane combat-aircraft designs. The introduction of the advanced A5M "Claude" fighters into the Shanghai-Nanjing theater of operations, beginning on 18 September 1937, helped the Japanese achieve a certain level of air superiority. However the few experienced Chinese veteran pilots, as well as several Chinese-American volunteer fighter pilots, including Maj. Art Chin, Maj. John Wong Pan-yang, and Capt. Chan Kee-Wong, even in their older and slower biplanes, proved more than able to hold their own against the sleek A5Ms in dogfights, and it also proved to be a battle of attrition against the Chinese Air Force. At the start of the battle, the local strength of the NRA was around five divisions, or about 70,000 troops, while local Japanese forces comprised about 6,300 marines. On 23 August, the Chinese Air Force attacked Japanese troop landings at Wusongkou in northern Shanghai with Hawk III fighter-attack planes and P-26/281 fighter escorts, and the Japanese intercepted most of the attack with A2N and A4N fighters from the aircraft carriers Hosho and Ryujo, shooting down several of the Chinese planes while losing a single A4N in the dogfight with Lt. Huang Xinrui in his P-26/281; the Japanese Army reinforcements succeeded in landing in northern Shanghai. The Imperial Japanese Army (IJA) ultimately committed over 300,000 troops, along with numerous naval vessels and aircraft, to capture the city. After more than three months of intense fighting, their casualties far exceeded initial expectations. On 26 October, the IJA captured Dachang, a key strong-point within Shanghai, and on 5 November, additional reinforcements from Japan landed in Hangzhou Bay. Finally, on 9 November, the NRA began a general retreat.

Japan did not immediately occupy the Shanghai International Settlement or the Shanghai French Concession, areas which were outside of China's control due to the treaty port system. Japan moved into these areas after its 1941 declaration of war against the United States and the United Kingdom.

Battle of Nanjing and massacre

In November 1937, the Japanese concentrated 220,000 soldiers and began a campaign against Nanjing. Building on the hard-won victory in Shanghai, the IJA advanced on and captured the KMT capital city of Nanjing (December 1937) and Northern Shanxi (September – November 1937).

Japanese forces inflicted heavy casualties on the Chinese soldiers defending the city, killing approximately 50,000 of them including 17 Chinese generals. Upon the capture of Nanjing, Japanese committed massive war atrocities including mass murder and rape of Chinese civilians after 13 December 1937, which has been referred to as the Nanjing Massacre. Over the next several weeks, Japanese troops perpetrated numerous mass executions and tens of thousands of rapes. The army looted and burned the surrounding towns and the city, destroying more than a third of the buildings.

The number of Chinese killed in the massacre has been subject to much debate, with estimates ranging from 100,000 to more than 300,000. The numbers agreed upon by most scholars are provided by the International Military Tribunal for the Far East, which estimate at least 200,000 murders and 20,000 rapes.

The Japanese atrocities in Nanjing, especially following the Chinese defense of Shanghai, increased international goodwill for the Chinese people and the Chinese government.

The Nationalist government re-established itself in Chongqing, which became the wartime seat of government until 1945.

1938

By January 1938, most conventional Kuomintang forces had either been defeated or no longer offered major resistance to Japanese advances. KMT forces won a few victories in 1938 (the Battle of Taierzhuang and the Battle of Wanjialing) but were generally ineffective that year. By March 1938, the Japanese controlled almost all of North China. Communist-led rural resistance to the Japanese remained active, however.

Battles of Xuzhou and Taierzhuang

With many victories achieved, Japanese field generals escalated the war in Jiangsu in an attempt to wipe out the Chinese forces in the area. The Japanese managed to overcome Chinese resistance around Bengbu and the Teng xian, but were fought to a halt at Linyi.

The Japanese were then decisively defeated at the Battle of Taierzhuang (March–April 1938), where the Chinese used night attacks and close quarters combat to overcome Japanese advantages in firepower. The Chinese also severed Japanese supply lines from the rear, forcing the Japanese to retreat in the first Chinese victory of the war.

The Japanese then attempted to surround and destroy the Chinese armies in the Xuzhou region with an enormous pincer movement. However the majority of the Chinese forces, some 200,000-300,000 troops in 40 divisions, managed to break out of the encirclement and retreat to defend Wuhan, the Japanese's next target.

Battle of Wuhan

Following Xuzhou, the IJA changed its strategy and deployed almost all of its existing armies in China to attack the city of Wuhan, which had become the political, economic and military center of China, in hopes of destroying the fighting strength of the NRA and forcing the KMT government to negotiate for peace. On 6 June, they captured Kaifeng, the capital of Henan, and threatened to take Zhengzhou, the junction of the Pinghan and Longhai railways.

The Japanese forces, numbering some 400,000 men, were faced by over 1 million NRA troops in the Central Yangtze region. Having learned from their defeats at Shanghai and Nanjing, the Chinese had adapted themselves to fight the Japanese and managed to check their forces on many fronts, slowing and sometimes reversing the Japanese advances, as in the case of Wanjialing.

To overcome Chinese resistance, Japanese forces frequently deployed poison gas and committed atrocities against civilians, such as a "mini-Nanjing Massacre" in the city of Jiujiang upon its capture. After four months of intense combat, the Nationalists were forced to abandon Wuhan by October, and its government and armies retreated to Chongqing. Both sides had suffered tremendous casualties in the battle, with the Chinese losing up to 500,000 soldiers killed or wounded,</ref> and the Japanese up to 200,000.

Communist resistance

After their victory at Wuhan, Japan advanced deep into Communist territory and redeployed 50,000 troops to the Shanxi-Chahar-Hebei Border Region. Elements of the Eighth Route Army soon attacked the advancing Japanese, inflicting between 3,000 and 5,000 casualties and resulting in a Japanese retreat. The Eighth Route Army carried out guerilla operations and established military and political bases. As the Japanese military came to understand that the Communists avoided conventional attacks and defense, it altered its tactics. The Japanese military built more roads to quicken movement between strongpoints and cities, blockaded rivers and roads in an effort to disrupt Communists supply, sought to expand militia from its puppet regime to conserve manpower, and use systematic violence on civilians in the Border Region in an effort to destroy its economy. The Japanese military mandated confiscation of the Eighth Route Army's goods and used this directive as a pretext to confiscate goods, including engaging in grave robbery in the Border Region.

With Japanese casualties and costs mounting, the Imperial General Headquarters attempted to break Chinese resistance by ordering the Imperial Japanese Navy Air Service and Imperial Japanese Army Air Service to launch the war's first massive air raids on civilian targets. Japanese raiders hit the Kuomintang's newly established provisional capital of Chongqing and most other major cities in unoccupied China, leaving many people either dead, injured, or homeless.

Yellow River flood

The 1938 Yellow River flood (simplified Chinese: 花园口决堤事件; traditional Chinese: 花園口決堤事件; pinyin: Huāyuánkǒu Juédī Shìjiàn; lit. 'Huayuankou Dam Burst Incident') was a man-made flood from June 1938 to January 1947 created by the intentional destruction of levees on the Yellow River in Huayuankou, Henan by the National Revolutionary Army (NRA) during the Second Sino-Japanese War. The first wave of floods hit Zhongmu County on 13 June 1938.

1939–1940: Chinese counterattack and stalemate

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By 1939, the Nationalist army had withdrawn to the southwest and northwest of China and the Japanese controlled the coastal cities that been centres of Nationalist power. From 1939 to 1945, China was divided into three regions: Japanese-occupied territories (Lunxianqu), the Nationalist-controlled region (Guotongqu), and the Communist-controlled regions (Jiefangqu, or liberated areas).

From the beginning of 1939, the war entered a new phase with the unprecedented defeat of the Japanese at Battle of Suixian–Zaoyang and First Battle of Changsha. These outcomes encouraged the Chinese to launch their first large-scale counter-offensive against the IJA in December 1939; however, due to its low military-industrial capacity and limited experience in modern warfare, this offensive was defeated. Afterwards Chiang could not risk any more all-out offensive campaigns given the poorly trained, under-equipped, and disorganized state of his armies and opposition to his leadership both within the Kuomintang and in China in general. He had lost a substantial portion of his best trained and equipped troops in the Battle of Shanghai and was at times at the mercy of his generals, who maintained a high degree of autonomy from the central KMT government.

During the offensive, Hui forces in Suiyuan under generals Ma Hongbin and Ma Buqing routed the Imperial Japanese Army and their puppet Inner Mongol forces and prevented the planned Japanese advance into northwest China. Ma Hongbin's father Ma Fulu had fought against Japanese in the Boxer Rebellion. General Ma Biao led Hui, Salar and Dongxiang cavalry to defeat the Japanese at the Battle of Huaiyang. Ma Biao fought against the Japanese in the Boxer Rebellion.

After 1940, the Japanese encountered tremendous difficulties in administering and garrisoning the seized territories, and tried to solve their occupation problems by implementing a strategy of creating friendly puppet governments favourable to Japanese interests in the territories conquered. This included prominently the regime headed by Wang Jingwei, one of Chiang's rivals in the KMT. However, atrocities committed by the Imperial Japanese Army, as well as Japanese refusal to delegate any real power, left the puppets very unpopular and largely ineffective. The only success the Japanese had was to recruit a large Collaborationist Chinese Army to maintain public security in the occupied areas.

Japanese expansion

By 1941, Japan held most of the eastern coastal areas of China and Vietnam, but guerrilla fighting continued in these occupied areas. Japan had suffered high casualties which resulted from unexpectedly stubborn Chinese resistance, and neither side could make any swift progress in the manner of Nazi Germany in Western Europe.

By 1943, Guangdong had experienced famine. As the situation worsened, New York Chinese compatriots received a letter stating that 600,000 people were killed in Siyi by starvation.

Second phase: October 1938 – December 1941

During this period, the main Chinese objective was to drag out the war for as long as possible in a war of attrition, thereby exhausting Japanese resources while it was building up China's military capacity. American general Joseph Stilwell called this strategy "winning by outlasting". The NRA adopted the concept of "magnetic warfare" to attract advancing Japanese troops to definite points where they were subjected to ambush, flanking attacks, and encirclements in major engagements. The most prominent example of this tactic was the successful defense of Changsha in 1939, and again in the 1941 battle, in which heavy casualties were inflicted on the IJA.

Local Chinese resistance forces, organized separately by both the CCP and the KMT, continued their resistance in occupied areas to make Japanese administration over the vast land area of China difficult. In 1940, the Chinese Red Army launched a major offensive in north China, destroying railways and a major coal mine. These constant guerilla and sabotage operations deeply frustrated the Imperial Japanese Army and they led them to employ the Three Alls Policy—kill all, loot all, burn all. It was during this period that the bulk of Japanese war crimes were committed.

By 1941, Japan had occupied much of north and coastal China, but the KMT central government and military had retreated to the western interior to continue their resistance, while the Chinese communists remained in control of base areas in Shaanxi. In the occupied areas, Japanese control was mainly limited to railroads and major cities ("points and lines"). They did not have a major military or administrative presence in the vast Chinese countryside, where Chinese guerrillas roamed freely.

From 1941 to 1942, Japan concentrated most of its forces in China in an effort to defeat the Communist bases behind Japan's lines. To decrease guerilla's human and material resources, the Japanese military implemented its Three Alls policy ("Kill all, loot all, burn all"). In response, the Communist armies increased their role in production activities, including farming, raising hogs, and cloth-making.

Relationship between the Nationalists and the Communists

After the Mukden Incident in 1931, Chinese public opinion was strongly critical of Manchuria's leader, the "young marshal" Zhang Xueliang, for his non-resistance to the Japanese invasion, even though the Kuomintang central government was also responsible for this policy, giving Zhang an order to improvise while not offering support. After losing Manchuria to the Japanese, Zhang and his Northeast Army were given the duty of suppressing the Red Army in Shaanxi after their Long March. This resulted in great casualties for his Northeast Army, which received no support in manpower or weaponry from Chiang Kai-shek.

In the Xi'an Incident that took place on 12 December 1936, Zhang Xueliang kidnapped Chiang Kai-shek in Xi'an, hoping to force an end to KMT–CCP conflict. To secure the release of Chiang, the KMT agreed to a temporary ceasefire with the Communists. On 24 December, the two parties agreed to a United Front against Japan; this had salutary effects for the beleaguered Communists, who agreed to form the New Fourth Army and the 8th Route Army under the nominal control of the NRA. In addition, Shaan-Gan-Ning and Shanxi-Chahar-Hebei border regions were created, under the control of the CCP. In Shaan-Gan-Ning, Communists in the Shaan-Gan-Ning Base Area fostered opium production, taxed it, and engaged in its trade—including selling to Japanese-occupied and KMT-controlled provinces. The Red Army fought alongside KMT forces during the Battle of Taiyuan, and the high point of their cooperation came in 1938 during the Battle of Wuhan.

The formation of a united front added to the legality of the CCP, but what kind of support the central government would provide to the communists were not settled. When compromise with the CCP failed to incentivize the Soviet Union to engage in an open conflict against Japan, the KMT withheld further support for the Communists. To strengthen their legitimacy, Communist forces actively engaged the Japanese early on. These operations weakened Japanese forces in Shanxi and other areas in the North. Mao Zedong was distrustful of Chiang Kai-shek, however, and shifted strategy to guerrilla warfare in order to preserve the CCP's military strength.

Despite Japan's steady territorial gains in northern China, the coastal regions, and the rich Yangtze River Valley in central China, the distrust between the two antagonists was scarcely veiled. The uneasy alliance began to break down by late 1938, partially due to the Communists' aggressive efforts to expand their military strength by absorbing Chinese guerrilla forces behind Japanese lines. Chinese militia who refused to switch their allegiance were often labelled "collaborators" and attacked by CCP forces. For example, the Red Army led by He Long attacked and wiped out a brigade of Chinese militia led by Zhang Yin-wu in Hebei in June 1939. Starting in 1940, open conflict between Nationalists and Communists became more frequent in the occupied areas outside of Japanese control, culminating in the New Fourth Army Incident in January 1941.

Afterwards, the Second United Front completely broke down and Chinese Communists leader Mao Zedong outlined the preliminary plan for the CCP's eventual seizure of power from Chiang Kai-shek. Mao himself is quoted outlining the "721" policy, saying "We are fighting 70 percent for self development, 20 percent for compromise, and 10 percent against Japan". Mao began his final push for consolidation of CCP power under his authority, and his teachings became the central tenets of the CCP doctrine that came to be formalized as Mao Zedong Thought. The Communists also began to focus most of their energy on building up their sphere of influence wherever opportunities were presented, mainly through rural mass organizations, administrative, land and tax reform measures favouring poor peasants; while the Nationalists attempted to neutralize the spread of Communist influence by military blockade of areas controlled by CCP and fighting the Japanese at the same time.

Entrance of the Western Allies

Japan had expected to extract economic benefits of its invasions of China and elsewhere, including in the form of fuel and raw material resources. As Japanese aggression continued, however, the United States responded with trade embargoes on various goods, including oil and petroleum (beginning December 1939) and scrap iron and munitions (beginning July 1940). The United States demanded that Japan withdraw from China and also refused to recognize Japan's occupations of the Indochinese countries. In spring 1941, trade negotiations between the United States and Japan failed. In July 1941, the United States froze Japanese financial assets and obtained Dutch and British agreements to also cut those countries' oil exports to Japan. This in turn prompted the Japanese decision to attack Pearl Harbor.

Following the attack on Pearl Harbor, the United States declared war against Japan, and within days China joined the Allies in formal declaration of war against Japan, Germany and Italy. As the Western Allies entered the war against Japan, the Sino-Japanese War would become part of a greater conflict, the Pacific theatre of World War II. Japan's military action against the United States also restrained its capacity to conduct further offensive operations in China.

After the Lend-Lease Act was passed in 1941, American financial and military aid began to trickle in. Claire Lee Chennault commanded the 1st American Volunteer Group (nicknamed the Flying Tigers), with American pilots flying American warplanes which were painted with the Chinese flag to attack the Japanese. He headed both the volunteer group and the uniformed U.S. Army Air Forces units that replaced it in 1942. However, it was the Soviets that provided the greatest material help for China from 1937 into 1941, with fighter aircraft for the Nationalist Chinese Air Force and artillery and armour for the Chinese Army through the Sino-Soviet Treaty; Operation Zet also provided for a group of Soviet volunteer combat aviators to join the Chinese Air Force in the fight against the Japanese occupation from late 1937 through 1939. The United States embargoed Japan in 1941 depriving it of shipments of oil and various other resources necessary to continue the war in China. This pressure, which was intended to disparage a continuation of the war and bring Japan into negotiation, resulted in the Attack on Pearl Harbor and Japan's drive south to procure from the resource-rich European colonies in Southeast Asia by force the resources which the United States had denied to them.

Almost immediately, Chinese troops achieved another decisive victory in the Battle of Changsha, which earned the Chinese government much prestige from the Western Allies. President Franklin D. Roosevelt referred to the United States, United Kingdom, Soviet Union and China as the world's "Four Policemen"; his primary reason for elevating China to such a status was the belief that after the war it would serve as a bulwark against the Soviet Union.

Knowledge of Japanese naval movements in the Pacific was provided to the American Navy by the Sino-American Cooperative Organization (SACO) which was run by the Chinese intelligence head Dai Li. Philippine and Japanese ocean weather was affected by weather originating near northern China. The base of SACO was located in Yangjiashan.

Chiang Kai-shek continued to receive supplies from the United States. However, in contrast to the Arctic supply route to the Soviet Union which stayed open through most of the war, sea routes to China and the Yunnan–Vietnam Railway had been closed since 1940. Therefore, between the closing of the Burma Road in 1942 and its re-opening as the Ledo Road in 1945, foreign aid was largely limited to what could be flown in over "The Hump". In Burma, on 16 April 1942, 7,000 British soldiers were encircled by the Japanese 33rd Division during the Battle of Yenangyaung and rescued by the Chinese 38th Division. After the Doolittle Raid, the Imperial Japanese Army conducted a massive sweep through Zhejiang and Jiangxi, now known as the Zhejiang-Jiangxi Campaign, with the goal of finding the surviving American airmen, applying retribution on the Chinese who aided them and destroying air bases. The operation started 15 May 1942, with 40 infantry battalions and 15–16 artillery battalions but was repelled by Chinese forces in September. During this campaign, the Imperial Japanese Army left behind a trail of devastation and also spread cholera, typhoid, plague and dysentery pathogens. Chinese estimates allege that as many as 250,000 civilians, the vast majority of whom were destitute Tanka boat people and other pariah ethnicities unable to flee, may have died of disease. It caused more than 16 million civilians to evacuate far away deep inward China. 90% of Ningbo's population had already fled before battle started.

Most of China's industry had already been captured or destroyed by Japan, and the Soviet Union refused to allow the United States to supply China through the Kazakhstan into Xinjiang as the Xinjiang warlord Sheng Shicai had turned anti-Soviet in 1942 with Chiang's approval. For these reasons, the Chinese government never had the supplies and equipment needed to mount major counter-offensives. Despite the severe shortage of matériel, in 1943, the Chinese were successful in repelling major Japanese offensives in Hubei and Changde.

Chiang was named Allied commander-in-chief in the China theater in 1942. American general Joseph Stilwell served for a time as Chiang's chief of staff, while simultaneously commanding American forces in the China-Burma-India Theater. For many reasons, relations between Stilwell and Chiang soon broke down. Many historians (such as Barbara W. Tuchman) have suggested it was largely due to the corruption and inefficiency of the Kuomintang government, while others (such as Ray Huang and Hans van de Ven) have depicted it as a more complicated situation. Stilwell had a strong desire to assume total control of Chinese troops and pursue an aggressive strategy, while Chiang preferred a patient and less expensive strategy of out-waiting the Japanese. Chiang continued to maintain a defensive posture despite Allied pleas to actively break the Japanese blockade, because China had already suffered tens of millions of war casualties and believed that Japan would eventually capitulate in the face of America's overwhelming industrial output. For these reasons the other Allies gradually began to lose confidence in the Chinese ability to conduct offensive operations from the Asian mainland, and instead concentrated their efforts against the Japanese in the Pacific Ocean Areas and South West Pacific Area, employing an island hopping strategy.

Long-standing differences in national interest and political stance among China, the United States, and the United Kingdom remained in place. British Prime Minister Winston Churchill was reluctant to devote British troops, many of whom had been routed by the Japanese in earlier campaigns, to the reopening of the Burma Road; Stilwell, on the other hand, believed that reopening the road was vital, as all China's mainland ports were under Japanese control. The Allies' "Europe first" policy did not sit well with Chiang, while the later British insistence that China send more and more troops to Indochina for use in the Burma Campaign was seen by Chiang as an attempt to use Chinese manpower to defend British colonial possessions. Chiang also believed that China should divert its crack army divisions from Burma to eastern China to defend the airbases of the American bombers that he hoped would defeat Japan through bombing, a strategy that American general Claire Lee Chennault supported but which Stilwell strongly opposed. In addition, Chiang voiced his support of the Indian independence movement in a 1942 meeting with Mohandas Gandhi, which further soured the relationship between China and the United Kingdom.

American and Canadian-born Chinese were recruited to act as covert operatives in Japanese-occupied China. Employing their racial background as a disguise, their mandate was to blend in with local citizens and wage a campaign of sabotage. Activities focused on destruction of Japanese transportation of supplies (signaling bomber destruction of railroads, bridges). Chinese forces advanced to northern Burma in late 1943, besieged Japanese troops in Myitkyina, and captured Mount Song. The British and Commonwealth forces had their operation in Mission 204 which attempted to provide assistance to the Chinese Nationalist Army. The first phase in 1942 under command of SOE achieved very little, but lessons were learned and a second more successful phase, commenced in February 1943 under British Military command, was conducted before the Japanese Operation Ichi-Go offensive in 1944 compelled evacuation.

1944 and Operation Ichi-Go

In 1944, the Communists launched counteroffensives from the liberated areas against Japanese forces.

Japan's 1944 Operation Ichi-Go was the largest military campaign of the Second Sino-Japanese War. The campaign mobilized 500,000 Japanese troops, 100,000 horses, 1,500 artillery pieces, and 800 tanks. The 750,000 casualty figure for Nationalist Chinese forces are not all dead and captured, Cox included in the 750,000 casualties that China incurred in Ichigo soldiers who simply "melted away" and others who were rendered combat ineffective besides killed and captured soldiers.

In late November 1944, the Japanese advanced slowed approximately 300 miles from Chongqing as it experienced shortages of trained soldiers and materiel. Although Operation Ichi-Go achieved its goals of seizing United States air bases and establishing a potential railway corridor from Manchukuo to Hanoi, it did so too late to impact the result of the broader war. American bombers in Chengdu were moved to the Mariana Islands where, along with bombers from bases in Saipan and Tinian, they could still bomb the Japanese home islands.

After Operation Ichigo, Chiang Kai-shek started a plan to withdraw Chinese troops from the Burma theatre against Japan in Southeast Asia for a counter offensive called "White Tower" and "Iceman" against Japanese soldiers in China in 1945.

The poor performance of Chiang Kai-shek's forces in opposing the Japanese advance during Operation Ichigo became widely viewed as demonstrating Chiang's incompetence. It irreparably damaged the Roosevelt administration's view of Chiang and the KMT. The campaign further weakened the Nationalist economy and government revenues. Because of the Nationalists' increasing inability to fund the military, Nationalist authorities overlooked military corruption and smuggling. The Nationalist army increasingly turned to raiding villages to press-gang peasants into service and force marching them to assigned units. Approximately 10% of these peasants died before reaching their units.

By the end of 1944, Chinese troops under the command of Sun Li-jen attacking from India, and those under Wei Lihuang attacking from Yunnan, joined forces in Mong-Yu, successfully driving the Japanese out of North Burma and securing the Ledo Road, China's vital supply artery. In Spring 1945 the Chinese launched offensives that retook Hunan and Guangxi. With the Chinese army progressing well in training and equipment, Wedemeyer planned to launch Operation Carbonado in summer 1945 to retake Guangdong, thus obtaining a coastal port, and from there drive northwards toward Shanghai. However, the atomic bombings of Hiroshima and Nagasaki and Soviet invasion of Manchuria hastened Japanese surrender and these plans were not put into action.

Chinese industrial base and the CIC

Foreign aid

Before the start of full-scale warfare of the Second Sino-Japanese War, Germany had since the time of the Weimar Republic, provided much equipment and training to crack units of the National Revolutionary Army of China, including some aerial-combat training with the Luftwaffe to some pilots of the pre-Nationalist Air Force of China. A number of foreign powers, including the Americans, Italians and Japanese, provided training and equipment to different air force units of pre-war China. With the outbreak of full-scale war between China and the Empire of Japan, the Soviet Union became the primary supporter for China's war of resistance through the Sino-Soviet Non-Aggression Pact from 1937 to 1941. When the Imperial Japanese invaded French Indochina, the United States enacted the oil and steel embargo against Japan and froze all Japanese assets in 1941, and with it came the Lend-Lease Act of which China became a beneficiary on 6 May 1941; from there, China's main diplomatic, financial and military supporter came from the U.S., particularly following the attack on Pearl Harbor.

Overseas Chinese

Over 3,200 overseas Chinese drivers and motor vehicle mechanics embarked to wartime China to support military and logistics supply lines, especially through Indo-China, which became of absolute tantamount importance when the Japanese cut-off all ocean-access to China's interior with the capture of Nanning after the Battle of South Guangxi. Overseas Chinese communities in the U.S. raised money and nurtured talent in response to Imperial Japan's aggressions in China, which helped to fund an entire squadron of Boeing P-26 fighter planes purchased for the looming war situation between China and the Empire of Japan; over a dozen Chinese-American aviators, including John "Buffalo" Huang, Arthur Chin, Hazel Ying Lee, Chan Kee-Wong et al., formed the original contingent of foreign volunteer aviators to join the Chinese air forces (some provincial or warlord air forces, but ultimately all integrating into the centralized Chinese Air Force; often called the Nationalist Air Force of China) in the "patriotic call to duty for the motherland" to fight against the Imperial Japanese invasion. Several of the original Chinese-American volunteer pilots were sent to Lagerlechfeld Air Base in Germany for aerial-gunnery training by the Chinese Air Force in 1936.

German

Prior to the war, Germany and China were in close economic and military cooperation, with Germany helping China modernize its industry and military in exchange for raw materials. Germany sent military advisers such as Alexander von Falkenhausen to China to help the KMT government reform its armed forces. Some divisions began training to German standards and were to form a relatively small but well trained Chinese Central Army. By the mid-1930s about 80,000 soldiers had received German-style training. After the KMT lost Nanjing and retreated to Wuhan, Hitler's government decided to withdraw its support of China in 1938 in favour of an alliance with Japan as its main anti-Communist partner in East Asia.

Soviet

After Germany and Japan signed the anti-communist Anti-Comintern Pact, the Soviet Union hoped to keep China fighting, in order to deter a Japanese invasion of Siberia and save itself from a two-front war. In September 1937, they signed the Sino-Soviet Non-Aggression Pact and approved Operation Zet, the formation of a secret Soviet volunteer air force, in which Soviet technicians upgraded and ran some of China's transportation systems. Bombers, fighters, supplies and advisors arrived, headed by Aleksandr Cherepanov. Prior to the Western Allies, the Soviets provided the most foreign aid to China: some $250 million in credits for munitions and other supplies. The Soviet Union defeated Japan in the Battles of Khalkhin Gol in May – September 1939, leaving the Japanese reluctant to fight the Soviets again. In April 1941, Soviet aid to China ended with the Soviet–Japanese Neutrality Pact and the beginning of the Great Patriotic War. This pact enabled the Soviet Union to avoid fighting against Germany and Japan at the same time. In August 1945, the Soviet Union annulled the neutrality pact with Japan and invaded Manchuria, Inner Mongolia, the Kuril Islands, and northern Korea. The Soviets also continued to support the Chinese Communist Party. In total, 3,665 Soviet advisors and pilots served in China, and 227 of them died fighting there.

The Soviet Union provided financial aid to both the Communists and the Nationalists.

United States

The United States generally avoided taking sides between Japan and China until 1940, providing virtually no aid to China in this period. For instance, the 1934 Silver Purchase Act signed by President Roosevelt caused chaos in China's economy which helped the Japanese war effort. The 1933 Wheat and Cotton Loan mainly benefited American producers, while aiding to a smaller extent both Chinese and Japanese alike. This policy was due to US fear of breaking off profitable trade ties with Japan, in addition to US officials and businesses perception of China as a potential source of massive profit for the US by absorbing surplus American products, as William Appleman Williams states.

From December 1937, events such as the Japanese attack on USS Panay and the Nanjing Massacre swung public opinion in the West sharply against Japan and increased their fear of Japanese expansion, which prompted the United States, the United Kingdom, and France to provide loan assistance for war supply contracts to China. Australia also prevented a Japanese government-owned company from taking over an iron mine in Australia, and banned iron ore exports in 1938. However, in July 1939, negotiations between Japanese Foreign Minister Arita Khatira and the British Ambassador in Tokyo, Robert Craigie, led to an agreement by which the United Kingdom recognized Japanese conquests in China. At the same time, the US government extended a trade agreement with Japan for six months, then fully restored it. Under the agreement, Japan purchased trucks for the Kwantung Army, machine tools for aircraft factories, strategic materials (steel and scrap iron up to 16 October 1940, petrol and petroleum products up to 26 June 1941), and various other much-needed supplies.

In a hearing before the United States Congress House of Representatives Committee on Foreign Affairs on Wednesday, 19 April 1939, the acting chairman Sol Bloom and other Congressmen interviewed Maxwell S. Stewart, a former Foreign Policy Association research staff and economist who charged that America's Neutrality Act and its "neutrality policy" was a massive farce which only benefited Japan and that Japan did not have the capability nor could ever have invaded China without the massive amount of raw material America exported to Japan. America exported far more raw material to Japan than to China in the years 1937–1940. According to the United States Congress, the U.S.'s third largest export destination was Japan until 1940 when France overtook it due to France being at war too. Japan's military machine acquired war materials, automotive equipment, steel, scrap iron, copper, oil, that it wanted from the United States in 1937–1940 and was allowed to purchase aerial bombs, aircraft equipment, and aircraft from America up to the summer of 1938. A 1934 U.S. State Department memo even noted how Japan's business dealings with Standard Oil of New Jersey company, under the leadership of Walter Teagle, made United States oil the "major portion of the petroleum and petroleum products now imported into Japan." War essentials exports from the United States to Japan increased by 124% along with a general increase of 41% of all American exports from 1936 to 1937 when Japan invaded China. Japan's war economy was fueled by exports to the United States at over twice the rate immediately preceding the war. According to the U.S. Department of Commerce, Japan corresponded to the following share of American exports.

Japan invaded and occupied the northern part of French Indochina in September 1940 to prevent China from receiving the 10,000 tons of materials delivered monthly by the Allies via the Haiphong–Yunnan Fou Railway line.

On 22 June 1941, Germany attacked the Soviet Union. In spite of non-aggression pacts or trade connections, Hitler's assault threw the world into a frenzy of re-aligning political outlooks and strategic prospects.

On 21 July, Japan occupied the southern part of French Indochina (southern Vietnam and Cambodia), contravening a 1940 gentlemen's agreement not to move into southern French Indochina. From bases in Cambodia and southern Vietnam, Japanese planes could attack Malaya, Singapore, and the Dutch East Indies. As the Japanese occupation of northern French Indochina in 1940 had already cut off supplies from the West to China, the move into southern French Indochina was viewed as a direct threat to British and Dutch colonies. Many principal figures in the Japanese government and military (particularly the navy) were against the move, as they foresaw that it would invite retaliation from the West.

On 24 July 1941, Roosevelt requested Japan withdraw all its forces from Indochina. Two days later the US and the UK began an oil embargo; two days after that the Netherlands joined them. This was a decisive moment in the Second Sino-Japanese War. The loss of oil imports made it impossible for Japan to continue operations in China on a long-term basis. It set the stage for Japan to launch a series of military attacks against the Allies, including the attack on Pearl Harbor on 7 December 1941.

In mid-1941, the United States government financed the creation of the American Volunteer Groups (AVG), of which one the "Flying Tigers" reached China, to replace the withdrawn Soviet volunteers and aircraft. The Flying Tigers did not enter actual combat until after the United States had declared war on Japan. Led by Chennault, their early combat success of 300 kills against a loss of 12 of their newly introduced Curtiss P-40 Warhawk fighters heavily armed with six 0.50-inch caliber machine guns and very fast diving speeds earned them wide recognition at a time when the Chinese Air Force and Allies in the Pacific and SE Asia were suffering heavy losses, and soon afterwards their "boom and zoom" high-speed hit-and-run air combat tactics would be adopted by the United States Army Air Forces.

Disagreements existed both between the United States and the Nationalists, and within the United States military, about the form of aid. Chennault contended that aid should be in the form of building on the success of the Flying Tigers and go to the US Fourteenth Air Force in China. Lieutenant General Joseph Stilwell, who was in charge of training Nationalist divisions equipped by the United States, became increasingly frustrated by the Nationalists' refusal to use them to fight the Japanese in Burma or in southeastern China.

The Sino-American Cooperative Organization was an organization created by the SACO Treaty signed by the Republic of China and the United States of America in 1942 that established a mutual intelligence gathering entity in China between the respective nations against Japan. It operated in China jointly along with the Office of Strategic Services (OSS), America's first intelligence agency and forerunner of the CIA while also serving as joint training program between the two nations. Among all the wartime missions that Americans set up in China, SACO was the only one that adopted a policy of "total immersion" with the Chinese. The "Rice Paddy Navy" or "What-the-Hell Gang" operated in the China-Burma-India theater, advising and training, forecasting weather and scouting landing areas for USN fleet and Gen Claire Chennault's 14th AF, rescuing downed American flyers, and intercepting Japanese radio traffic. An underlying mission objective during the last year of war was the development and preparation of the China coast for Allied penetration and occupation. Fujian was scouted as a potential staging area and springboard for the future military landing of the Allies of World War II in Japan.

United Kingdom

After the Tanggu Truce of 1933, Chiang Kai-Shek and the British government would have more friendly relations but were uneasy due to British foreign concessions there. During the Second Sino-Japanese War the British government would initially have an impartial viewpoint toward the conflict urging both to reach an agreement and prevent war. British public opinion would swing in favor of the Chinese after Hughe Knatchbull-Hugessen's car which had Union Jacks on it was attacked by Japanese aircraft with Hugessen being temporarily paralyzed with outrage against the attack from the public and government. The British public were largely supportive of the Chinese and many relief efforts were untaken to help China. Britain at this time was beginning the process of rearmament and the sale of military surplus was banned but there was never an embargo on private companies shipping arms. A number of unassembled Gloster Gladiator fighters were imported to China via Hong Kong for the Chinese Air Force. Between July 1937 and November 1938 on average 60,000 tons of munitions were shipped from Britain to China via Hong Kong. Attempts by the United Kingdom and the United States to do a joint intervention were unsuccessful as both countries had rocky relations in the interwar era.

In February 1941 a Sino-British agreement was forged whereby British troops would assist the Chinese "Surprise Troops" units of guerrillas already operating in China, and China would assist Britain in Burma.

When Hong Kong was overrun in December 1941, the British Army Aid Group (B.A.A.G.) was set up and headquartered in Guilin, Guangxi. It's aim was to assist prisoners of war and internees to escape from Japanese camps. This led to the formation of the Hong Kong Volunteer Company which later fought in Burma. B.A.A.G. also sent agents to gather intelligence – military, political and economic in Southern China, as well as giving medical and humanitarian assistance to Chinese civilians and military personnel.

A British-Australian commando operation, Mission 204 (Tulip Force), was initialized to provide training to Chinese guerrilla troops. The mission conducted two operations, mostly in the provinces of Yunnan and Jiangxi.

The first operation commenced in February 1942 from Burma on a long journey to the Chinese front. Due to issues with supporting the Chinese and gradual disease and supply issues, the first phase achieved very little and the unit was withdrawn in September.

Another phase was set up with lessons learned from the first. Commencing in February 1943 this time valid assistance was given to the Chinese 'Surprise Troops' in various actions against the Japanese. These involved ambushes, attacks on airfields, blockhouses, and supply depots. The unit operated successfully before withdrawal in November 1944.

Commandos and members of SOE who had formed Force 136, worked with the Free Thai Movement who also operated in China, mostly while on their way into Thailand.

After the Japanese blocked the Burma Road in April 1942, and before the Ledo Road was finished in early 1945, the majority of US and British supplies to the Chinese had to be delivered via airlift over the eastern end of the Himalayan Mountains known as "The Hump". Flying over the Himalayas was extremely dangerous, but the airlift continued daily to August 1945, at great cost in men and aircraft.

French Indochina

The Chinese Kuomintang also supported the Vietnamese Việt Nam Quốc Dân Đảng (VNQDD) in its battle against French and Japanese imperialism. In Guangxi, Chinese military leaders were organizing Vietnamese nationalists against the Japanese. The VNQDD had been active in Guangxi and some of their members had joined the KMT army. Under the umbrella of KMT activities, a broad alliance of nationalists emerged. With Ho at the forefront, the Viet Nam Doc Lap Dong Minh Hoi (Vietnamese Independence League, usually known as the Viet Minh) was formed and based in the town of Jingxi. The pro-VNQDD nationalist Ho Ngoc Lam, a KMT army officer and former disciple of Phan Bội Châu, was named as the deputy of Phạm Văn Đồng, later to be Ho's Prime Minister. The front was later broadened and renamed the Viet Nam Giai Phong Dong Minh (Vietnam Liberation League).