@mattbiernat:
Do you guys think that U.S. was capable of invading and controlling Soviet Union for long enough to impose a Democracy? […] Assuming U.S.A. did not develop atomic bomb.
No, both from a physical and a political viewpoint.
Germany failed to defeat the USSR in 1941, despite the fact that after the partition of Poland was Russia’s next-door neighbor, that Russia’s military preparedness wasn’t what it should have been, and that Germany and her allies invaded with almost 4 million troops. America is about 3,000 miles across the Atlantic from Europe (to which you have to add the distance to get from France to Russia), so geographically it would have been in a much less advantageous position to attack Russia than Germany was. Its armies were also comparatively small compared to Russia’s, which by 1945 had (as I recall) some 300 divisions in Europe and had been hardened by four years of war with Nazi Germany.
As for the political angle, I don’t see how Truman could have persuaded the war-weary American public and America’s servicemen – after four years of propaganda films hailing the Soviets as heroic allies in the fight against fascism – to suddenly turn against the Russians right after the Nazis had been beaten. Just look at the reaction of the victorious American troops in Europe, who were dismayed to learn that they would be transferred to the Pacific to help finish the war against Japan, which was already an enemy country – a war in which, incidentally, Stalin had agreed to join in early August (which he did).
The A-bomb, by the way, isn’t a significant variable in this equation. The US was only able to develop three bombs in 1945, one of which was expended in the Trinity test. The two others sufficed to shock Japan – which by mid-1945 was on its last legs – into surrendering, but they would not have allowed the US to conquer Russia. The USSR absorbed some 20 million dead during the war with Germany without collapsing (in fact, it emerged from the war as a huge military power), so even if America had nuked Moscow and Leningrad and killed some 100,000 Russians, the USSR’s reaction would not have been to surrender. More probably, its reaction would have been to send its 300 European divisions storming into western Europe in a fit of outrage at having been treacherously attacked by its former Anglo-American allies.