The Allies, formally referred to as the United Nations from 1942, were an international military coalition formed during World War II (1939–1945) to oppose the Axis powers. Its principal members by the end of 1941 were the "Big Four" – the United Kingdom, United States, Soviet Union, and China.

Allied powers, coalition of countries that opposed the Axis powers (led by Germany, Italy, and Japan) during World War II. The principal members of the Allies were the United Kingdom, the Soviet Union, the United States, and China (the “Big Four”), as well as France while it was unoccupied.

World War II [b] or the Second World War (1 September 1939 – 2 September 1945) was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all the world's countries—including all the great powers—participated, with many investing all available economic, industrial, and scientific capabilities in pursuit of total war, blurring the distinction between military and ...

All the Axis powers were defeated in the course of World War II and left the conflict at different times. Mussolini was deposed following the invasion of Sicily in 1943, and Italy formally changed sides and joined the Allies later that year, though Rome would not be liberated until June 1944.