when did usa turn up in the 2nd world war

June 30, 2026

The USA entered World War II in December 1941 , after Japan attacked Pearl Harbor on December 7, 1941 ; Congress declared war on December 8, 1941. Germany and Italy then declared war on the U.S. on December 11, 1941 , bringing America fully into the war.

Quick Scoop

Attack: Pearl Harbor, December 7, 1941

U.S. declaration of war on Japan: December 8, 1941

Germany and Italy declare war on the U.S.: December 11, 1941

In plain terms, the U.S. "turned up" in the war at the end of 1941 , not earlier.

TL;DR

The U.S. officially joined World War II on December 8, 1941 , the day after Pearl Harbor was attacked.