Thank the Soviet Union as well.
http://en.wikipedia.org/wiki/Operation_barbarossa#Aftermath
The Red Army absolutely crushed the Germans on the Eastern Front, driving them from the Volga River all the way back to Berlin - which the Soviets ultimately took. Not the Americans. The American War effort was nothing less that crucial in defeating Hitler, yes - but they did not win the war singlehandedly. Far from it. "Learning all history" should really mean learning all history.
The kid should know Iwo Jima though.
Didn't exactly crush them outright, they won through sheer numbers, attrition and determination. But yes, a few americans should know that it wasn't them who won the war alone