The Allies were the countries united in an alliance in World War II
(1939–45) to fight the Axis countries of Germany, Japan, and Italy. The
countries that first declared war on Germany after its invasion of Poland
in 1939 were the founding Allied forces. They were Poland, Great
Britain, and France.
Many countries joined the Allied efforts over the course of the war.
Twenty-six countries signed the Declaration by the United Nations on
January 1, 1942, uniting them in the Allied cause. More nations would
sign later.
The leading efforts of Great Britain, the Soviet Union, and the
United States in the second half of the war earned them the distinction
as “the Big Three.” Prime Minister Winston Churchill (1874–1965) of
Great Britain, Premier Joseph Stalin (1879–1953) of the Soviet Union,
and President Franklin D. Roosevelt (1882–1945; served 1933–45) of
the United States coordinated the military efforts of the Allies across the world. China and France, the latter when not occupied by Germany and
its Nazi dictator, Adolf Hitler (1889–1945), played important leading
roles as well.
The Allies managed to defeat the Axis powers even though their resources were stretched around the world. After the capture of Italy’s dictator, Benito Mussolini (1883–1945), Italy switched sides to fight with
the Allies in September 1943. The battles across Europe ended with the
unconditional surrender of Germany on May 7, 1945. Battles around
the Pacific Ocean against Japan continued until the United States used
the atomic bomb for the first time to end the war. After suffering the
devastation of the cities Hiroshima and Nagasaki, Japan agreed to surrender on August 10, 1945.