America was part of the Allies in World War II, fighting against the Axis Powers. The primary members of the Axis Powers alliance were Germany, Japan and Italy.
In 1940, Germany, Italy and Japan had signed the Tripartite Pact, and as a group they became known as the Axis Powers. Hungary, Bulgaria, and Romania were also aligned with the Axis Powers.
The Axis Powers fought against the Allied Powers. The main countries making up the Allied Powers were Great Britain, France, the Soviet Union, and the United States. Other countries that were part of the Allied Powers were Poland, China, Australia, New Zealand, Canada, Netherlands, Yugoslavia, Belgium, and Greece.