This was the start of WWII for America.   The lost of life was large but not compared to what was coming!  The Reason Japan bombed Pearl Harbor was to destroy the Battleships which at time was the principal ship for war.  Japan wanted the US Navy out of the way so Japan could invade SE ASIA and not able to stop Japans war with China. So in a way the start of war also for SE Asia as Japan attacked the Philippines just hours later but because of the time difference was on the 8th.

Attack on Pearl Harbor