I just realise I know next to nothing about what was happening in Japan prior to the 1937 Japanese invasion of China.

It seems like, leading up to 1937, there were series of political assassinations and military mutinies that kept pushing Japan politic into far right. Finally in 1937 the Japanese army in Manchu, literally out of control, started an attack on Chinese territory which immediately escalated to a full scale war. Japanese at the time supported the invasion because of both the poor economic condition at home and ambition of land-grab as inspired by Hitler of Nazi Germany.

Should study more about this time period in Asia.