when did the us join ww2

The United States entered World War II in December 1941, after the Japanese attack on Pearl Harbor.

Quick Scoop

• Japan attacked Pearl Harbor on 7 December 1941.

• The next day, 8 December 1941, the US declared war on Japan, marking its formal entry into World War II in the Pacific.

• On 11 December 1941, Germany and Italy declared war on the United States, and the US responded by declaring war on them the same day, bringing it fully into the wider conflict.

So, if someone asks “when did the US join WW2,” most historians point to early December 1941—starting with the attack on Pearl Harbor on 7 December and the US declaration of war on Japan on 8 December, followed by war with Germany and Italy on 11 December.

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