The Japanese Navy was spotted leaving Japan over a week in advance of Pearl Harbor, by the Australian navy.

The US Pacific fleet was made up of older WW1 and inter-war era ships that were quickly getting outpaced by the new SuperBattleships of the era, such as the Bismarck and Yamato.

The fleet stationed at Hawaii conspicuously had no carriers, those expensive ships had been relocated months earlier to the east coast.

Before Pearl Harbor, US public opinion on entering "Europe's War" was in the single digits, since the public still remembered the pointless slog that was WW1. After Pearl Harbor public sentiment was bent towards revenge, as intended.

Japan's attack plan involved sending midget subs into the harbor on Saturday so they could torpedo ships on Sunday during the attack, but the subs were intercepted and fired upon that Saturday afternoon. No warning was made to the naval base of an impending attack.

The crippled Pacific fleet was replaced in 13 months following the issuing of lucrative contracts to shipbuilding companies, at lower cost than scrapping the older ships.

Pearl Harbor was an inside job.
So was the USS Maine, so was the Gulf of Tonkin incident, so was every war since the Barbary ones.