Question

One reason for the outbreak of world war II was the

Answer 1

Japan had already taken over Korea, Manchuria, and a significant part of China before World War 2 had started.

Answer 2

Okay one big reason, you don't have to go further then Hitler. The "cause" to his power was because of the political failure of the Wiemar Public which was imposed on Germany in 1919.
Hope I got it correct!