But how could Truman have saved thousands of American lives if, as GUEST,Displaced Camelotian says:

Planned or not, had the war not ended when it did, Stalin's army would have invaded Japan in early September, before our own planned invasion.

If this is true, then it would have been Soviet soldiers who would have been killed rather than Americans. So now I'm wondering if maybe the US nuked Japan specifically for the purpose of preventing the Soviets from invading it first.