World War II was fought between the Allied Powers (led by Britain, France, the Soviet Union, and the United States) and the Axis Powers (led by Germany, Italy, and Japan). Some key events leading up to the war included Germany, Italy and Japan's aggression in the 1930s, which the League of Nations failed to stop. In 1938, Germany annexed Austria and gained control of Czechoslovakia's Sudetenland through the Munich Pact. In 1939, Germany invaded Poland, marking the official start of World War II.