Pearl Harbor was the incident (shortly after the sinking of the Lusitania) that catalyzed America's inevitable entry into the war. There was a very strong isolationist mindset before this period, which mean America simply did not want to be involved much in world affairs at all, let alone take on a leadership role.

I agree that the attack, and the sinking of America's warships touched a nerve with the public. Americans loved their warships and were very proud of them, and an attack on them simply incensed people.