Second Sino-Japanese War background
First Sino-Japanese War
The orgin of the Second-Sino Japanese War can be traced to the First Sino-japanese war of 1894-1895
In 1915, Japan issued the Twenty-One Demands to extort further political and commercial privilege from China.
This battle culminated in the Jinan Incident of 1928 in which the and the Imperial Japanese Army were engaged in a short conflict that resulted in the Kuomintang's withdrawal from Jinan
Nominal Unification of China
In the same year Zhang Zuolin was assassinated when he became less willing to cooperate with Japan
Communist Party of China
In 1930, large-scale civil war broke out between warlords who had fought in alliance with the Kuomintang during the Northern Expedition and the central government under Chiang.
Then the Invasion of Manchuria, interventions in China