When World War I ended in 1918, it was called, the war to end all wars. But it wasn't. Unsettled issues and resentments festered for the next 20 years, culminating in the outbreak of war in Europe and Asia in the 1930s. The Axis powers, led by Germany, Italy, and Japan, joined to fight the Allies, led by the U.S., the United Kingdom, and the Soviet Union. Both sides were determined to rule the world, but only one can succeed.