Why didn't america join the european war before 1941

Which fact would this be, and how might you verify the truth?

What was the goal of the united states' invasion at the bay of pigs?

Why was it decided in potsdam that certain industries in germany would be disabled? a. to deplete resources that might prevent germany from coming to power again b. so that a portion of the eastern region of poland would be fused together with the soviet union c. to allow the allies to focus their war efforts in fighting the last part of the war against japan d. to provide economic aid for iran's government since large war demands were made on them