Why do american think they won WWII?

here's my point. England holded firm against the Nazi's alone for quite a time. then America was attacked, and they smashed in the West of Europe. true. but 60% of the german troop, 70% of the luftwaffe and 65% of the tanks and trucks were fighting the USSR. I never hear an american giving them credit. so please, why do americans seem to think they won the ar, while they fought less than half of the german troops, with the help of the other Allies, while the USSR army was doing more from the east than America with the other Allies from the West?