Why did the United States enter World War II?

Answers from the USCIS list

Give one of these answers. Words in light (parentheses) are optional.

• optional: (Bombing of) Pearl Harbor
• Japanese attacked Pearl Harbor
• To support the Allied Powers optional: (England, France, and Russia)
• To oppose the Axis Powers optional: (Germany, Italy, and Japan)

Our explanation

On December 7, 1941, Japan attacked Pearl Harbor, a U.S. Navy base in Hawaii. Then the U.S. entered the war. It joined the Allied Powers (England, France, and Russia) against the Axis Powers (Germany, Italy, and Japan).

Remember it

Japan attacked Pearl Harbor, so the U.S. entered WWII. Axis: Germany, Italy, Japan.

Source

USCIS 2025 Study Guide (M-1175) p. 64: “On December 7, 1941, Japan attacked the United States at a U.S. naval base in Hawaii called Pearl Harbor.” Allied/Axis lists from M-1778 (09/25) Q106.

• 128 Civics Questions and Answers (2025 version), M-1778 (09/25) (PDF, USCIS)

Last checked on September 29, 2026.

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Easy to mix up with

• 101Why did the United States enter World War I?