Nazi Germany would have been defeated without military involvement from the USA. Russian forces would have advanced most of the way to coast of France, most likely.
The A-Bomb did not win the war. Due to the superior production capacity of the USA Japan would have been defeated without its use.
The defining moment of the pacific campaign was the battle of Midway. This, as agreed by hundreds of military analysts, was a 1 in a million chance win for the American forces. Any reasonable estimate would have had the Japanese forces decimate the Americans at this battle hence putting the Japanese in control of the pacific theater in naval terms. Fortunately the American forces where exceptionally lucky and through a series of highly improbable events disabled the main Japanese carrier fleet. Its a damn good thing it happened but theres no way it should have happened that way.
The only necessary US involvment in the western front was that of factory output/ financial aid. The war would have been won without US military involvement, however Europe would look very different today.
Edit: Do not even think to use "we". You had nothing to do with it. "They" would be a much more appropriate word to use. It is the sacrifice of men and women from many countries, not just America, who defeated Nazi Germany, something that you personally had absolutely nothing to do with. Be respectful of these people.