What event marked the beginning of U.S. involvement in World War II?

The attack on Pearl Harbor on December 7, 1941, marked the beginning of U.S. involvement in World War II. On this day, Japanese forces launched a surprise military strike against the United States naval base at Pearl Harbor in Hawaii. The attack resulted in significant loss of life and damage to the Pacific Fleet, and it prompted the U.S. government to declare war on Japan the following day, December 8, 1941.

This event shattered the prevailing isolationist sentiment in the United States, which had been reluctant to engage in overseas conflicts following World War I. The attack unified the American public and government in support of an active military response to the war. The subsequent declarations of war against Germany and Italy soon followed, cementing the U.S. role as a key player in the global conflict.

Other choices refer to significant events related to World War I and World War II but do not represent the moment when the United States formally entered the conflict. The signing of the Treaty of Versailles pertains to the conclusion of World War I, while the D-Day invasion and the bombing of Hiroshima occurred later in World War II, representing major turning points and actions rather than the initial entry into the war.