Japanese airplanes, above, attacks the ships by surprises killed and injured many troops on December 7th, 1941.
Co-prosperity Sphere Strategy
FDR freezes all Japanese assets in America from the Japanese occupation of French Indochina.
Relied on the U.S. of about 80% worth of oil and without their navy couldn't operate properly. By attacking the U.S. it would cripple and destroy the Pacific fleet so it can take over islands.
Declartation for war
There was an idea to take over colonials holdings in Europe and the United States to become undefeated which succeeded by attacking U.S. territories, British Singapore, Hong Kong, and Malaya.
Though the U.S. was caught off guard, there was a decoded message by magic from the Japanese sent that day before the attack "to be on alert". But by some circumstances, it didn't arrive until after the attack.
The next following day, FDR announce that the United States of America declares war on Japan by firechats which the American people were wanting to do.