Which event marked the beginning of significant American involvement in World War II?

The bombing of Pearl Harbor is the event that marked the beginning of significant American involvement in World War II. On December 7, 1941, the Japanese launched a surprise military strike against the United States naval base at Pearl Harbor in Hawaii. This attack led to substantial casualties and damage to the U.S. Pacific Fleet, prompting a swift and unified response from the American public and government.

In the aftermath of the attack, the United States declared war on Japan the following day, which effectively brought the nation into the global conflict. The incident transformed American isolationist sentiments into a commitment to actively engage in the war effort against the Axis powers. It served as a pivotal moment that united the country and marked a significant turning point in the war, leading to the mobilization of American military forces and resources on a large scale.

The other events noted, such as the Fall of France and the Invasion of Normandy, occurred during the course of the war but did not directly result in the U.S. entering the conflict. The Battle of Britain was critical in the European theater, yet it also did not involve direct U.S. military engagement until after Pearl Harbor prompted U.S. involvement.