Japan had attacked the United States, this incident is called Pearl Harbour. This is when bombers from aircraft carriers attacked US navy ships. This strategy was the same used by the US navy during an exercise. The casualties ranged to 1500 - 2000. On December 8, the United States declared war.
In december 1941, pearl harbour was attacked inflicting large amounts of casualties onto the us navy which had caused the us to declare war on the Japanese.
