Why do American's think they won WW2 all by themselves?

I'm a British teenager and I'm taking History as a GCSE and I recently had a holiday In America and I have noticed that Americans are VERY proud and VERY patriotic over there accomplishments during the second World War. Fair enough us Brit's couldn't have won over Hitler without them but I'm fed up with Americans saying that they won it all by themselves and that no country can ever beat them. The truth is that the Russians played the biggest part in the war an without them everyone would now be speaking German.