I might as well go ahead and post this, because I'm going to be taking a break from forums for the next few weeks.
Leading up to the 1936 election, Roosevelt had come under quite a bit of fire from anti-communist groups and from canidates such as Landon (Republican), Father Coughlin & Gerald Smith, and ultimately William Lemke ("Union"), Alfred Smith (Liberty League) accusing Roosevelt's policies and ideas as being socialist (which, in some respects, they really were). That is fact. My theory (which I have heard echoed in private conversations) is that Roosevelt became a very public anti-communist supporter. It's not that much of a stretch to think that public opinion could sway someone's ideas and thoughts. Before now, he really didn't pay much attention to it. He was already against Fascism, so it ultimately became a choice between the lesser of two evils in his mind as WWII developed (especially when Guderian's brilliant attacks rendered half the continent under German control): If the Soviets fell, or worse, signed a treaty with Hitler, then a war with Germany could last 10 years, and the US still not win. Roosevelt had already decided to help Churchill (who did a brilliant job of gaining support) with the threats of a German invasion imminent upon the Isles. If they fell, the world's oceans would be the German's to control.
If Stalin decided to sign a treaty with Hitler, it would mean the immediate destruction of every Allied power currently in the war (Britian, it's colonies, and the Free French - remember, Hitler didn't declare on the US until December 11th). At best it would mean Japan, Germany, the US, and everything the Germans and Japanese wanted. At worse, it would mean the ultimate showdown between the Japanese and Germans teaming up on the US. Something we would not have survived, based upon the vast resources Russia, the ME and Indochina would have contributed to the war effort.
So, Roosevelt had to at least give Stalin a nugget. Something that would entice him to stay in the war. Roosevelt's agreement to provide supplies through Iran (although it would take about three months) combined with Hitler's absolute non-

ing knowledge about how to run a campaign led to the Soviet's survival through the winter of '41-'42 and ultimately to the Red Star being hoisted upon the Nazi Party buildings in Berlin. We got the wine (literally) and they got the Party HQ at the cost of 100k troops. C'est la vie, I suppose.
But Roosevelt (and particularly Churchill) didn't trust Stalin. Roosevelt thought him a nice enough guy (even calling him a 'nice Christian man' or something to the effect), but the Manhattan Project was definetly not going to be shared with Stalin, because the US and Britian wanted the upper hand in post-war politics. (Didn't see India coming, did you?) The Grand Alliance was not meant to last beyond WWII, and it wasn't going to. Because of the initial distrust of Stalin at the first meetings, it led to further rifts when Stalin made decisions that would fall away from the US's view.
On the Soviet side, there are a myriad of reasons why they hated the US specifically. First, the idea of the proletariat conflicted directly with the US economy and how it was designed to cater to the big business and entrepreneurs that existed in the 20s, and the 30s (in regards to the Rockefellers, etc). Communist doctrine (based on Marxism) decreed that farms and business belong to the people (read: the state) and individuals should not have what the masses could not. So, Lenin and Stalin had pounded that into the people (and if you didn't like it, it was death or Siberia). Furthermore, and more importantly, it was viewed that the US and Britian had delayed on purpose committing supplies and goods to the Soviet people and had let them take the brunt of the death, decay and damage brought upon by the German's attack. With Japan not revealing it's true motives until late in 1941, Stalin could not commit the Far Eastern units that would have probably repelled Hitler initially (given if his commanders had seen the Panzer strength of en masse attacks and not spreading out tanks along the front, that's a big if I know). But nevertheless, there was a growing resentment towards the end of the war that they had fought this war all by themselves...something that Stalin definetly didn't dissuage after he had learned about the secret nuclear development Roosevelt had even hidden from Churchill to some extent (specifically Project Alberta) and development between the US and UK.
And after the war, we know all the rest. The Berlin Airlift, and beyond. I've run out of time, and I'm going on pure memory, so don't crucify me if some of my facts are incorrect. A lot of my paper was fact, and the rest was extrapolated theory. Went down well, for what it's worth.
Anyways, so like I said, I'm going on a little hiatus to take care of some personal matters like my kids. So have fun in my absense.