World War II, also known as the Second World War, was a global conflict that lasted from 1939 to 1945. It involved the majority of the world's nations, including all of the great powers. The war was fought on two fronts, with the Allies (primarily the United States, Great Britain, and the Soviet Union) fighting against the Axis powers (primarily Germany, Japan, and Italy). Other synonyms for World War II include the Great Patriotic War, the War of Resistance Against Japan, and the Pacific War. Regardless of what it is called, World War II was a devastating period in human history that resulted in millions of deaths and significant geopolitical changes.