Political Map of Western and Eastern Theaters of WWII as in 1939

1939-01-01

The Causes of World War II, a global war from 1939 to 1945 that was the deadliest conflict in human history, have been given considerable attention by historians from many countries who studied and understood them. The immediate precipitating event was the invasion of Poland by Nazi Germany on September 1, 1939 and the subsequent declarations of war on Germany made by Britain and France, but many other prior events have been suggested as ultimate causes. Primary themes in historical analysis of the war's origins include the political takeover of Germany in 1933 by Adolf Hitler and the Nazi Party; Japanese militarism against China, which led to the Second Sino-Japanese War; Italian aggression against Ethiopia, which led to the Second Italo-Ethiopian War and Germany's initial success in negotiating the Molotov–Ribbentrop Pact with the Soviet Union to divide the territorial control of Eastern Europe between them.

Wikipedia: Causes of World War II