Roosevelt desparately wanted an attack so he could justify getting into the war after winning the election promising he wouldn’t. He participated with the British in locking Japan out of all their raw materials and energy supplies. At the time of Pearl Harbor, Japan had less than 9 months of oil left and no prospects of more and their raw material supplies were shut off.. FDR had spies on Japan mainland that let Washington know that the Japanese fleet had sailed to attack, so they knew it was pending. FDR then wanted to let Pearl Harbor know but without alarming the Japanese spies that were all over the place, lest the attack get called off and he lose his excuse to go to war. So they sent the alarm to Hawaii via regular correspondense mail, rather than as an emergency comunique, which might have raised alarm. Either would have had ships at sea where the attackers could not have found them. He desparately did not want Japan to call off the attack. And it only took a few errors and delays before that warning, that would have saved most of the 3000 lives lost, did not get there in time. Pearl Harbor was taken by surprise and with the port napping, although much of the fleet was by coincidence actually not there at the time. Those people were killed because FDR needed an excuse. They were collateral damage.
The minute that the attack occured, FDR jumped in with both feet and immediately declared war on Japan and also with Germany who had a treaty of support with Japan, and then just as immediateyl ramped up the war machine and began official massive support of the war in Europe, which he had to do minimally and covertly up til then.
Wish I didn’t know this.