allied nations; alliance of countries
General term for a group of nations united by a treaty or common cause. Not limited to the World Wars.
The treaty formed an alliance of nations.
the Allies; Allied powers
Specifically refers to the Allied powers in World War I and World War II. Often contrasted with 枢軸国 (the Axis powers).
See also: 枢軸国
In World War II, the Allies fought against the Axis powers.