Third and fourth terms of the presidency of Franklin D. Roosevelt
On the morning of December 7, 1941, the Japanese struck the U.S. naval base at Pearl Harbor with a surprise attack, knocking out the main American battleship fleet and killing 2,403 American servicemen and civilians. The great majority of scholars have rejected the conspiracy thesis that Roosevelt, or any other high government officials, knew in advance about the Japanese attack on Pearl Harbor. The Japanese had kept their secrets closely guarded, and while senior American officials were aware that war was imminent, they did not expect an attack on Pearl Harbor. Roosevelt had anticipated that the first attack would take place in the Dutch East Indies, Thailand, or the Philippines.
Pearl Harbor
Following the overthrow of the Hawaiian Kingdom, the United States Navy established a base on the island in 1899. On December 7, 1941, the base was attacked by the Imperial Japanese Navy airplanes and midget submarines, causing the American entry into World War II. One of the main reasons that Pearl Harbor happened was because the United States had major communication breakdowns among several branches of the U.S. armed services and departments of the U.S. government. This led to the surprise Japanese attack at the Hawaiian air base. There was no meaningful plan for the air defense of Hawaii, for American commanders had no understanding of the capabilities and proper employment of air power. As it was, had the Pacific Fleet acted on the war warnings it undoubtedly would have sortied and been at sea on December 7, where the major ships would have been sunk in deep water, making salvage impossible. 
Shortly after the devastating Japanese surprise attack at Pearl Harbor two American military commanders, Lt. Gen. Walter Short and Adm. Husband Kimmel were demoted of their full ranks. The two American commanders later sought to restore their reputations and full ranks.