The major event in World War II known for the attack on Pearl Harbor occurred on December 7, 1941. On this fateful day, the Japanese military launched a surprise air raid on the U.S. naval base at Pearl Harbor in Hawaii, aiming to neutralize the Pacific Fleet and prevent American interference in Japan's expansionist activities in Southeast Asia. The attack resulted in significant losses, including the sinking of several battleships and the deaths of over 2,400 Americans. This event propelled the United States into World War II, leading to a declaration of war against Japan on December 8, 1941, and ultimately altering the course of the conflict.