World War II was fought between two military alliances.
 Many new designs, and concepts were used in combat, and all existing technologies of warfare were improved between 1939 and 1945
=== Second World War ===The Second World War occurred from 1939 to 1945 and is the only conflict in which nuclear weapons have been used; both Hiroshima and Nagasaki, in the Japanese Empire, were devastated by atomic bombs dropped by the United States

