The Japanese attacked Pearl Harbor on December 7, 1941 as a preemptive strike against the United States. The attack was supposed to be three waves of Japanese planes, but only two were sent out because the attack appeared to be very effective. This attack was intended to wipe out a large portion of the United State's navy, yet luckily for America, the aircraft carriers were not in Pearl Harbor on December 7th. Because of this America was able to recover more quickly than the Japanese anticipated when fighting in the Pacific Theater. Therefore, some consider the preemptive strike Japan's biggest mistake.
Before this point the United States considered themselves to be neutral. Yet some historians argue that the United States were not neutral before Pearl Harbor, due to the Lend-Lease Act on March 11, 1941. This act gave Franklin D. Roosevelt the power to sell or lend equipment to any country using them against the Axis powers. It can be argued that this appeared to be a threat towards Japan, (an Axis power) which in turn led to a Japanese preemptive strike. Therefore, after the December 7th attack, America was willing to open war with Japan in the Pacific Theater.
Another key point to examine is the mindset of America. Japan did not follow "proper" conduct and did not declare war on the United States before attacking. In result the people of America were outraged by what they considered an unprovoked attack. After Pearl Harbor, there was an increase in conscription to the army in preparation for war with Japan. Franklin D. Roosevelt's Presidential Address to Congress on December 8, 1941 was a response to the attack claiming that Pearl Harbor was a "date which will live in infamy" which only fueled American thirst for revenge. Later on December 8th, war was declared on Japan with no regard to peace negotiations.
Some historians argue that America would have still declared war on the Japanese, even if there was not an attack on Pearl Harbor. The reasoning is that the expansion of Imperial Japan would have eventually reached Australia, something that the United States would not agree with.
I hope this helped you a little bit! The historiography of World War II has so many different layers and perspectives.
