Any two of the big 3 (US, SU, UK+commonwealth), plus all the partisans and smaller allies could have done it. It was a dumb hopeless war that the Nazis picked because their ideology was incompatible with accurately evaluating their opponents.

But, it is good that all of the allies decided to band together and get it down a little bit faster. Every moment that Europe spent occupied was just another mountain of human suffering. Plus, getting that theater done before nukes really became available probably saved some historical German cities.