the war (1939-45) between the Allies (Great Britain, France, the Soviet Union, the U.S., etc.) and the Axis (Germany, Italy, Japan, etc.)
See World War II in American Heritage Dictionary 4
noun Abbr. WWII
A war fought from 1939 to 1945, in which Great Britain, France, the Soviet Union, the United States, China, and other allies defeated Germany, Italy, and Japan.