The main consequence of the Japanese attack on Pearl Harbor on December 7, 1941, was the United States' formal entry into World War II. Prior to the attack, the U.S. had maintained a stance of neutrality while providing support to Allied powers. The surprise assault on the naval base in Hawaii led to significant loss of life and damage to the Pacific Fleet. Following the attack, President Franklin D. Roosevelt delivered his famous "Day of Infamy" speech, prompting Congress to declare war on Japan the next day. This event significantly altered the course of the war and shaped international relations for decades to come.