Oops, wrong section. Sorry.
WW2 Discussion Thread TWO!

Some believe the Mukden Incident in 1931to be the beginning of WW2. Japanese soldiers tried to sabotage a rail line in China, blamed it on the Chinese, and used it as an excuse to invade Manchuria. This directly led to the Second Sino-Japanese War which started in 1937. That conflict pitted China, with aid from Russia and the United States, against Japan. Thus at least three of the world's major powers were already in conflict before the pot boiled over in Europe.
Titles says it all.