Why did the Japanese attack the United States at Pearl Harbor?

The attack commenced at 7:48 a.m. Hawaiian Time (18:18 GMT).[nb 4][16] The base was attacked by 353[17] Imperial Japanese aircraft (including fighters, level and dive bombers, and torpedo bombers) in two waves, launched from six aircraft carriers.[17] Of the eight U.S. Navy battleships present, all were damaged, with four sunk. All but USS Arizona were later raised, and six were returned to service and went on to fight in the war.