1) During the 1930s, totalitarian governments led by Hitler, Mussolini, and military leaders in Japan rose to power in Europe and Asia.
2) German expansionism under Hitler led to the start of World War II in Europe in 1939. Germany invaded Poland and later conquered Western Europe.
3) The United States initially remained neutral but joined the Allies after Japan's attack on Pearl Harbor in 1941, bringing the U.S. fully into World War II.