Who did the United States fight in World War II?

The United States fought against Japan, Germany, and Italy during World War II, which aligns with the historical alliances and adversaries of that conflict. The war began with Japan's attack on Pearl Harbor in December 1941, prompting the U.S. to enter the conflict primarily in the Pacific Theater against Japan. Concurrently, the U.S. was involved in the European Theater, where it fought against Germany and its Axis partner, Italy.

These three nations, Japan, Germany, and Italy, were the principal members of the Axis Powers, and their militaristic ambitions led to widespread conflict in multiple regions. The U.S. played a significant role in several key battles and operations against these countries, eventually contributing to their defeat and the end of the war in 1945.

Other choices include alliances or countries that were either not part of the Axis Powers or present nations during the conflict in different capacities, thus they do not accurately reflect the opponents the U.S. faced during World War II.