In what way was Hitler responsible for the onset of the 2nd world war?
Hitler was the cause of World War II. After the war, it was found that Hitler's goal was to take Western Russia, for German expansion. He started by testing Europe's mettle with the Anschluss in Austria, and then the negotiation for Czechoslovakia's Sudetenland in Munich. To assuage Russian worries about German expansion and buy time to acquire European resources, Hitler signed a Non-Agression pact in 1939 that gave Russia the Eastern half of Poland, and both sides promised peace with each other for at least 10 years.
Neville Chamberlain had drawn the proverbial line in the sand at Munich: the Polish border. Both Britain and France vowed to come to Poland's aid if Poland were invaded. Hitler knew that invading Poland would start the war, but he didn't care. September 1, 1939 World War II officially began in Europe. After eliminating most European resistance to the West (Britain was the only one left) Hitler turned his attention Eastward. He violated the Non-Aggression pact and invaded the Soviet Union in June 1941. This brought the Soviet Union into the war. When the USA declared war on Japan on Dec. 8, 1941, Hitler responded per terms of the Axis treaty, and Declared War on the USA Dec. 11, 1941.