What was the main reason why the US officially joined WWII on the Allies side all of these the surprise attack at Pearl Harbor

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What was the main reason why the US officially joined WWII on the Allies side all of these the surprise attack at Pearl Harbor in Hawaii on December 7th 1941 killing Americans and destroying American ships and airplanes the Zimmerman Telegram was intercepted and the US was worried that Germany was attempting to get Mexico to attack from the so the US was concerned that Germany was close to creating and using an atomic bomb in Europe

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