The Republic of China was founded in 1912, following the Xinhai Revolution which overthrew the last imperial dynasty of China, the Qing dynasty (1644–1911).
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. Japan invaded Manchuria outright after the Mukden Incident in September 1931.
Incessant fighting followed the Mukden Incident. In 1932, Chinese and Japanese troops fought the January 28 Incident battle. This resulted in the demilitarisation of Shanghai, which forbade the Chinese from deploying troops in their own city. In Manchukuo there was an ongoing campaign to defeat the Anti-Japanese Volunteer Armies that arose from widespread outrage over the policy of non-resistance to Japan.
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.
In 1933, the Japanese attacked the Great Wall region. The Tanggu Truce established in its aftermath, gave Japan control of Jehol province as well as a demilitarized zone between the Great Wall and Beiping-Tianjin region. Japan aimed to create another buffer zone between Manchukuo and the Chinese Nationalist government in Nanjing.
In 1935, under Japanese pressure, China signed the He–Umezu Agreement, which forbade the KMT from conducting party operations in Hebei.
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 May 12, 1936. Japan provided all the necessary military and economic aid.
On December 12, 1936, a deeply disgruntled Zhang Xueliang kidnapped Chiang Kai-shek in Xi'an, hoping to force an end to the conflict between KMT and CPC. To secure the release of Chiang, the KMT agreed to a temporary end to the Chinese Civil War .
On December 24, the creation of a United Front between the CPC and KMT against Japan. The alliance having salutary effects for the beleaguered CPC, they agreed to form the New Fourth Army and the 8th Route Army and place them under the nominal control of the NRA.
In 1937, the Japanese Imperial Army quickly marched into the heart of Chinese territory. On June 6, they captured Kaifeng, the capital of Henan, and threatened to take Zhengzhou, the junction of the Pinghan and Longhai railways.
On the night of July 7, 1937, Chinese and Japanese troops exchanged fire in the vicinity of the Marco Polo (or Lugou) Bridge, a crucial access-route to Beijing. What began as confused, sporadic skirmishing soon escalated into a full-scale battle in which Beijing and its port city of Tianjin fell to Japanese forces (July–August 1937).
On July 29, some 5,000 troops of the 1st and 2nd Corps of the East Hopei Army mutinied, turning against the Japanese garrison. In addition to Japanese military personnel, some 260 civilians living in Tongzhou in accordance with the Boxer Protocol of 1901, were killed in the uprising (predominantly Japanese including the police force and also some ethnic Koreans). The Chinese then set fire to and destroyed much of the city. Only around 60 Japanese civilians survived, who provided both journalists and later historians with firsthand witness accounts. As a result of the violence of the mutiny against Japanese civilians, the Tungchow mutiny, as it came to be called, strongly shook public opinion within Japan.
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 full-scale war. The KMT, however, determined that the "breaking point" of Japanese aggression had been reached. Chiang Kai-shek quickly mobilized the central government's army and air force, placed them under his direct command, and laid siege to the Japanese area of Shanghai International Settlement, where 30,000 Japanese civilians lived with 30,000 troops on August 12, 1937.
On August 13, 1937, Kuomintang soldiers and warplanes attacked Japanese Marine positions in Shanghai, leading to the Battle of Shanghai.
On August 14, Kuomintang planes accidentally bombed the Shanghai International Settlement, which led to more than 3,000 civilian deaths. In the three days from August 14 through 16, 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 Hawk III and P-26/281 Peashooter fighter squadrons.
In September 1937, the Soviet Union and China 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.
On August 23, Japanese Army reinforcements succeeded in landing in northern Shanghai. The Imperial Japanese Army (IJA) ultimately committed over 200,000 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 October 26, the Japanese Army captured Dachang, an important strong-point within Shanghai.
On November 5, additional reinforcements of Japan landed from Hangzhou Bay. Finally, on November 9, the NRA began a general retreat.
Building on the hard-won victory in Shanghai, the IJA captured the KMT capital city of Nanjing (December 1937) and Northern Shanxi (September–November 1937). These campaigns involved approximately 350,000 Japanese soldiers, and considerably more Chinese.
Historians estimate that between December 13, 1937, and late January 1938, Japanese forces killed an estimated 200,000 to 300,000 Chinese (mostly civilians) in the "Nanjing Massacre" (also known as the "Rape of Nanjing"), after its fall but the numbers are uncertain and possibly inflated coupled with the fact that the government of the People's Republic of China has never undertaken a full accounting of the Massacre.
With Japanese casualties and costs mounting, the Imperial General Headquarters attempted to break Chinese resistance by ordering the air branches of their navy and army 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 millions dead, injured, and homeless.
With many victories achieved, Japanese field generals escalated the war in Jiangsu in an attempt to wipe out Chinese resistance, but were defeated at the Battle of Taierzhuang (March–April 1938).
The Japanese captured Wuhan on October 27, 1938, forcing the KMT to retreat to Chongqing (Chungking), but Chiang Kai-shek still refused to negotiate, saying he would only consider talks if Japan agreed to withdraw to the pre-1937 borders.
From the beginning of 1939, the war entered a new phase with the unprecedented defeat of the Japanese at Battle of Suixian–Zaoyang, then 1st Battle of Changsha, Battle of South Guangxi and Battle of Zaoyi.
These outcomes encouraged the Chinese to launch their first large-scale counter-offensive against the IJA in early 1940; however, due to its low military-industrial capacity and limited experience in modern warfare, this offensive was defeated.
The uneasy alliance began to break down by late 1938. 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.
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.
In April 1941, Soviet aid 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.And in August 1945, the Soviet Union annulled the neutrality pact with Japan.
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. Almost immediately, Chinese troops achieved another decisive victory in the Battle of Changsha, which earned the Chinese government much prestige from the Western Allies.
A British-Australian commando operation, Mission 204, was initialized in February 1942 to provide training to Chinese guerilla troops. The mission conducted two operations, mostly in the provinces of Yunnan and Jiangxi. The first phase achieved very little but a second more successful phase was conducted before the withdrawal.
In Burma, on April 16, 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 of China, 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 May 15, 1942, with 40 infantry battalions and 15–16 artillery battalions but was repelled by Chinese forces in September.
Chinese forces invaded northern Burma in late 1943 besieged Japanese troops in Myitkyina and captured Mount Song.
In 1944, with the Japanese position in the Pacific deteriorating rapidly, the IJA mobilized over 500,000 men and launched Operation Ichi-Go, their largest offensive of World War II, to attack the American airbases in China and link up the railway between Manchuria and Vietnam. This brought major cities in Hunan, Henan and Guangxi under Japanese occupation.
In Spring 1945 the Chinese launched offensives that retook Hunan and Guangxi.
The United States and the Soviet Union put an end to the war by attacking the Japanese with a new weapon (on the United States' part) On August 6, 1945, an American B-29 bomber, the Enola Gay, dropped the first atomic bomb used in combat on Hiroshima, killing tens of thousands and leveling the city.
A Second equally destructive atomic bomb was dropped by the United States on Nagasaki.
On August 9, 1945, the Soviet Union renounced its non-aggression pact with Japan and attacked the Japanese in Manchuria.
In less than two weeks the Kwantung Army, which was the primary Japanese fighting force,consisting of over a million men but lacking in adequate armor, artillery, or air support, had been destroyed by the Soviets. Japanese Emperor Hirohito officially capitulated to the Allies on August 15, 1945.
The official surrender was signed aboard the battleship USS Missouri on September 2, 1945, in a ceremony where several Allied commanders including Chinese general Hsu Yung-chang were present.
After the Allied victory in the Pacific, General Douglas MacArthur ordered all Japanese forces within China (excluding Manchuria), Formosa and French Indochina north of 16° north latitude to surrender to Chiang Kai-shek, and the Japanese troops in China formally surrendered on September 9, 1945, at 9:00.