The major international conflict that involved the Axis Powers and the Allies was World War II, which occurred from 1939 to 1945. The Axis Powers, primarily Germany, Italy, and Japan, opposed the Allies, composed of nations like the United States, the United Kingdom, the Soviet Union, and China. This global conflict was marked by significant events such as the Holocaust, the use of atomic bombs on Hiroshima and Nagasaki, and the widespread fighting in Europe and the Pacific. The war resulted not only in immense human loss and destruction but also led to the establishment of the United Nations and the beginning of the Cold War.