Well here's a comic book cover illustrating Captain America in a one sided fight with Adolf Hitler.
To my knowledge stories of Captain America battling Nazis is a common theme for the Captain, at least much more than any other super heroes. I assume it has some sort of origins stemming from how all superheroes protect those that need to be protected from evil-doers. And in the real world the Nazis were committing genocide and other atrocities. The United States turned the tide of war and through story telling Captain America is an embodiment, a symbol, of America's intervention onto the war. So in summary the illustration above, of Captain America dealing a blow to Hitler, Captain America is representing America and Hitler represents the command and whole of the Axis forces. Thus taking into consideration the Nazi soldiers firing at Captain America to show how America mounted their advances in Europe against the native enemies. So America was directly responsible for the victory of the Allied forces.