Answer: World War II began in Europe on September 1, 1939, when Germany invaded Poland. Great Britain and France responded by declaring war on Germany on September 3
Explanation: Many historians argue that World War II began with the Marco Polo Bridge Incident on July 7, 1937. While other historians believe the war began with the Mukden Incident in Manchuria on September 18, 1931. Japanese occupation of much of Asia would last until 1945.
Some of the main points of this article are that Nationalism, Militarism, and territorial issues are some of the underlying causes of WWII.