You need to read a bit more history. The US was visibly arming for war
well before Pearl Harbor. It entered the war in Europe, for all practical
purposes, with the signing of the Lend-Lease treaty in early 1941.

The US oppinion did'nt want to interfere in the "European confict",
and only a "leasing deal" kept GB floating. In fact it has been
roumored that the ships were consentrated at PH to make it a tempting
carrot for the Japanese in order to turn public opinion.

Sincerely
Bjørn Ove