What significant event took place on December 7, 1941?

The significant event that occurred on December 7, 1941, was the attack on Pearl Harbor. This surprise military strike by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, led to the United States’ entry into World War II. The attack resulted in significant loss of life and damage to the Pacific Fleet, prompting President Franklin D. Roosevelt to call December 7 "a date which will live in infamy." This event was pivotal in shifting the balance of the war and led to a full-scale commitment of U.S. military forces in both the Pacific and European theaters.

The other options list events that are important in their own right but occur in different historical contexts. The Treaty of Versailles was signed in 1919 to officially end World War I. The D-Day invasion took place on June 6, 1944, as part of the Allied campaign to liberate Western Europe from Nazi control. The Korean War ended with an armistice signed in 1953, decades after the events of Pearl Harbor, further distinguishing the attack’s significance as a pivotal moment in U.S. military history.