The Japan-China War started in July 1937 when the Japanese claimed that they were fired on by Chinese troops at the Marco Polo Bridge near Beijing. Using this as an excuse, the Japanese launched a full-scale invasion of China using the conquered Manchuria as a launching base for their troops.
The Japanese came up against little organised resistance. The Guomintang put up little resistance though they were up against a formidable enemy. In November 1937, China's most important port, Shanghai, fell and Nanjing (Nanking), Chiang Kai-shek's capital, fell in December 1937.
The so-called “Rape of Nanking” has gone into the annals of history as one of the most shocking incidents in modern history. Its senior officers allowed the Japanese army to ransack Nanking murdering tens of thousands as they went. The final death toll for Nanjing has been put as high as 250,000. The Guomintang leader, Chiang, had to establish a new capital in Chongqing.
The onslaught of the Japanese was relentless. Within 5 months, 1 million Chinese people were under Japanese control. All of the major cities in China were captured by the Japanese by the end of 1937 - so were the major communication systems of the nation.
After this initial success, the Japanese did not advance much further into China. In many senses there was no reason for her to do so as most of China's hinterland contained nothing of strategic importance. Secondly, even the Japanese army could not hope to stretch its reserves to cover such a vast nation as China. By 1941, there were 2 million Japanese soldiers in China but even those areas captured by the Japanese were not totally controlled by them and this allowed the Chinese to gradually undermine the authority of the Japanese in this occupied zone.
The Japanese concentrated their efforts on the enemy they could see - the Guomintang. However, they also had to fight an enemy they could not see - communist guerrillas trained by Mao.
After Pearl Harbour in December 1941, the Japanese found that their army was even more stretched. The Americans sent supplies to the Chinese via the “Burma Road”. The enmity that existed between China and the west after 1949, was not apparent during the war. The American bombers that launched the first raid on Tokyo were scheduled to land in China. Airstrips were built in China to allow American planes to bomb Japanese shipping. In 1944, the Japanese started an all out attempt to occupy those parts of China that harboured American airbases. Though successful in that the Japanese captured Chiang's capital, Chongquig, it did not alter the outcome of the war.
The war against China had lead to 4 million Chinese casualties with 60 million made homeless.
The Japanese had spread out their forces too far and even the fanaticism of their approach to war could not stop the inevitable. The surrender of the Japanese in August 1945, left 1 million Japanese troops in China.
The Guomintang had borne the brunt of conventional fighting against the Japanese. This inevitably lead to casualties. Mao's fighters had perfected hit-and-run tactics against the Japanese which was to serve them well in the civil war that was to break out between the Guomintang and the Communists almost as soon as the war ended. The only thing that linked the Guomintang and Communists during the war was a common enemy. After the Japanese surrendered, each had to fight the other for supremacy in China.
By August 1945, the communists controlled far more of China than they had done in 1937. There were several reasons for this. The Japanese concentrated on an enemy they could 'see' and the Guomintang were the obvious enemy for the Japanese. Secondly, the communists continued with a policy of their soldiers helping the peasant population where they could, thus spreading the word of communism. In 1941, the Japanese started a campaign called the “Three All Campaign” which was designed to turn the peasants against the communists. It was a total failure.
The end of the war could only herald a full-scale clash between the Guomintang and the communists. It could only be a war to the end as neither was willing to tolerate the existence of the other.