Let us be honest. American contributions to the second World War were minimal at best and for the most part inconsequential.
Ahem.
Boeing B-17 Fortress
North American B-25 Mitchell
North American P-51 Mustang (A-36 Mustang to the boys in the RAF)
I'd say the United States' contribution to the war (even excepting the Pacific theater as we are doing) were quite considerable. US troops landed at Normandy on two of five beaches. Could the Allies have penetrated Europe with only 3/5 the force they had? Perhaps, but I'd have put more money on the defenders in that case.
I think Great Britain and the US have a much closer relationship politically, and have since D-Day because our boys were dying with theirs on D-Day. It's harder to forget when someone makes a sacrifice with you than when they make one for you.