World War II was caused by the outcome of World War I which humiliated and impoverished Germany, fueling nationalist sentiments. Germany, under Hitler, began rearming in violation of Treaty terms and invaded Poland in 1939, marking the start of WWII. Japan also expanded its military and attacked Pearl Harbor in 1941, drawing the U.S. into the war against the Axis powers of Germany, Italy and Japan. After several years of fighting around the globe, the Allied powers which included the U.S., Britain, Soviet Union and others defeated the Axis through massive invasions of Germany and Japan in 1944-1945, culminating in the U.S. atomic bombings of Hiroshima and Nagasaki that led