While the attack on Pearl Harbor was unprovoked, it is worth noting that rather than talk about it civilly, the U.S. decided to declare war on Japan. This leap in action takes away from the degree to which the U.S. ethically entered the war. There was no evidence to show that Japan intended on attacking again. The more righteous-- and thus more ethical--action to take would have been to diplomatically discuss the attack and come to an agreement that corrected the wrongs without going to war.
Most wars are entered because a perceived injustice. Many wars fought in the Middle East were fought because the United States' lack of oil was an injustice. Those wars were far from necessary, let alone ethical.