The conflict that historians would come to call the Second Sino-Japanese War was among the most destructive in human history. Stretching from 1937 to 1945, it consumed an entire continent, killed approximately 20 million people — the vast majority of them Chinese civilians — and served as the crucible in which the modern Chinese state was forged. Its origins lay in a deliberate act of deception, and its conclusion required the destruction wrought by atomic bombs and the entry of the Soviet Union to finally bring it to a close.
The seeds of the war were planted long before the first shots of the main conflict were fired. On September 18, 1931, officers of the Japanese Kwantung Army staged the Mukden Incident — a false flag operation in which Japanese agents sabotaged a section of the South Manchuria Railway and blamed the damage on Chinese soldiers. The manufactured provocation gave Japan the pretext it needed to invade Manchuria and establish the puppet state of Manchukuo the following year. This episode is sometimes identified as the true beginning of the war, preceding the larger conflict by six years. From 1931 to 1937, China and Japan engaged in a series of increasingly serious skirmishes in Shanghai and in northern China, as Japan steadily extended its influence and China struggled to respond.
China's political situation in these years was deeply fractured. The Nationalist government under Chiang Kai-shek and the Chinese Communist Party forces under Mao Zedong had been fighting each other in the Chinese Civil War since 1927. In late 1933, Chiang launched a major encirclement campaign against the Communists that drove them out of their southern bases and onto the Long March — an epic retreat during which Communist forces lost approximately ninety percent of their men. It was only as Japanese aggression became an existential threat that the two sides formed a United Front in 1936, a process accelerated by the Xi'an Incident, in which Chiang Kai-shek was briefly kidnapped by his own generals and pressured into cooperation.
The full-scale war began on July 7, 1937, following the Marco Polo Bridge Incident near Beijing, in which shots fired in a disputed nighttime encounter between Chinese and Japanese forces rapidly escalated into a general Japanese offensive. The Battle of Shanghai, one of the largest and most brutal urban battles of the entire conflict, lasted from August to November 1937 and demonstrated that Chinese forces could fight with tremendous tenacity even against a far more modern and well-supplied enemy. But the numbers told their own story, and Shanghai fell. Japanese forces then advanced on the Chinese capital, Nanjing, capturing it in December 1937. What followed — the systematic murder, rape, and torture of Chinese civilians and prisoners of war in what became known as the Nanjing Massacre — became one of the defining atrocities of the twentieth century and remains a deep wound in Chinese-Japanese relations to the present day.
Japan's advance continued in 1938 with the capture of Wuhan, which had served as China's de facto capital during the Nanjing campaign. After Wuhan fell, the Nationalist government relocated to Chongqing in the mountainous interior of Sichuan, placing it beyond the reach of Japanese ground forces but not of Japanese bombers. The Sino-Soviet Non-Aggression Pact, signed in 1937, brought significant Soviet military aid to China including aircraft, advisers, and equipment that bolstered the National Revolutionary Army and Air Force through the late 1930s. After Chinese victories at Changsha, with Japan's supply lines stretched deep into the interior, the conflict settled into a brutal stalemate by 1939.
In August 1940, Communist forces launched the Hundred Regiments Offensive, a massive guerrilla campaign in central China that demonstrated their continuing military vitality. Japan responded with scorched earth campaigns across North and Central China — operations that killed millions of civilians and destroyed the agricultural base of entire provinces. Soviet support ended abruptly in April 1941 with the Soviet-Japanese Neutrality Pact. Japan's attack on Pearl Harbor in December 1941 brought the United States into the conflict, and American Lend-Lease aid made the United States China's primary financial and military backer. When Japan cut the Burma Road, the main supply line to China, the United States Army Air Forces began airlifting supplies over the Himalayas along what pilots called the Hump — one of the most dangerous air routes in the history of aviation.
Japan's conduct of the war involved systematic atrocities that extended well beyond the battlefield. Its biological warfare program, Unit 731, carried out the largest biological weapons attacks in recorded history, causing at least 200,000 deaths in China through deliberate release of plague, typhoid, cholera, and other pathogens. Chemical weapons including lethal blister agents were used extensively against Chinese military and civilian targets. The scale of deliberate cruelty had few equivalents in modern warfare.
By 1944 the strategic tide was turning. Japan launched Operation Ichi-Go, a massive offensive in Henan and Changsha, to consolidate its position, but Chinese forces were growing more capable and better supplied. In 1945 the Chinese Expeditionary Force completed its advance through Burma, reopening overland supply routes via the Ledo Road. China launched major counteroffensives in the south, repelling a Japanese invasion of West Hunan and recapturing large portions of Guangxi. Japan's formal surrender on September 2, 1945 — following the atomic bombings of Hiroshima and Nagasaki and the Soviet declaration of war and invasion of Manchuria — brought the conflict to its close. China emerged as one of the Big Four Allied powers and became one of the five permanent members of the United Nations Security Council, regaining Taiwan and Manchuria. The civil war between Nationalists and Communists resumed in 1946, ending with the Communist victory in 1949. The eight years of resistance against Japan had shaped both the Communist Party's character and the Chinese national identity in ways that echoed for generations.
