What two things started World War 2?

The direct answer to this question is as follows: A. The German invasion of Poland on Sunday, September 1, 1939. B. By September 3, 1939 Britain and France held to their treaty to protect Poland and war was declared on Germany.

Germany fully expected this and already had created a strategy for the invasion of France.

These are the 2 things that began WW2. The circumstances that led up to WW2 are quite extensive and not pertinent to the question asked.