Answer:
American leaders calculated that the financial cost of the war would be too great to pay.
Step-by-step explanation:
The United States didn't join the war late, the United States didn't want to join world war II at all and there was no reasonable ground to do so.
Once Japan bombarded Pearl Harbor and announced war on America supported by Hitler, some say foolishly, revealing war two days later, the country's attitude changed 180 degrees and Roosevelt got his war.