The Japanese attack on the U.S. Pacific Fleet at Pearl Harbor on December 7, 1941, was one of the worst defeats in U.S. military history. It began a string of Japanese successes that seemed to threaten the security of the United States. Many U.S. citizens and government leaders were on the verge of panic. But the attack was probably the greatest mistake the Japanese made during World War II. At that time, many Americans didn t want to go to war. The anger and outrage that followed the attack swept away those objections. It unified the country and made the United States determined to win.