Incidentally, you might be very interested in a talk Max Hastings gave at Pritzker Military Library recently. At the end he gets asked some obnoxious question by a Stalin apologist and reminds the slug of the Molotov Ribbentrop Pact to shut him up. The MP3 is here.
Max Hastings is a British military historian, and the subject of the talk was Armageddon, his book about the end of World War II. I have not read the book, but the talk is excellent; and if the war interests you at all, you should spend the hour to listen to the talk. In the talk, Hastings makes a number of points about Stalin, the Red Army, its leaders, and its conduct in Poland after the war. Stalin, he says, was a far more effective warlord than was Hitler, largely because the Red Army's debacle to start the war taught him to leave all but the highest-level military questions to the men who actually knew about them, whereas Hitler never realized that he wasn't a military genius. He was a much more dangerous man for a general to work for, though, because he had a propensity for shooting generals, both because they failed and because they succeeded too well; Hitler, by contrast, didn't execute many of his army officers. The leaders of the Red Army by the end of the war, especially Georgy Zhukov, were the most effective generals of World War II, but they were effective largely because they were brutal and utterly unconcerned about the lives and well-being of their men. The Red Army was the most effective of the Allied armed forces, killing far more Germans and destroying far more German materiel than the Western Allies. Of course, their conduct in Germany at the end and after the war was nothing short of bestial, and they conducted a similarly brutal campaign after the war in Poland to exterminate all Poles who might object to Soviet domination. Listening to all of this, strangely enough, reminded me of why I can't stand William Shirer.
Shirer was the German correspondent for CBS radio for many years, ending with his expulsion from Germany in 1940. His Rise and Fall of the Third Reich, first published in 1959, remains the most widely-read popular history of the rise of the Nazi Party and the German conduct of World War II. Critics at the time and since have dismissed it as crude oversimplification of the Nazi era, but it is extremely readable; and I think that Shirer's opinions about the why the war came, even if not particularly original, were at the time and remain influential among the moderately well-read and well-educated American population. For Shirer, the causes of World War II are very simple: Germany fell under the control of a bunch of ruthless gangsters bent on world domination, and Britain and France were too cowardly to oppose them and too benighted by anti-Communist prejudice to recognize that alliance with the Soviet Union was, by the late 1930s, the only way to stop German aggression. He's certainly right about the first part: Germany did indeed fall under the control of a bunch of ruthless gangsters bent on world domination. The other two parts of his formulation are much more problematic. His account of British and French motivations for the policy of appeasement is much too simplistic and cartoonish, but that's not what I want to talk about here. It's his portrayal of the Soviet Union as the last, best hope of averting war.
On one level, Shirer is probably correct that an alliance between Britain, France, and the Soviet Union would have averted or at least delayed the beginning of World War II: had Hitler thought that the Soviets would have fought him if he invaded Poland, he probably wouldn't have invaded Poland on September 1, 1939. But what Shirer doesn't really address is whether the Soviets were negotiating with the Western Allies in good faith in 1939, whether it was really possible for them to have concluded an alliance on terms that would have been acceptable to both sides, and what the consequences of such an alliance would have been on the countries of Eastern Europe.
Was Stalin negotiating with the Western Allies in good faith in 1939? I doubt it. Leave aside the fact that Stalin had contemplated an accommodation with Hitler as early as 1936 during the Spanish Civil War, the fact that there was a history of German-Soviet cooperation dating to the 1920s, when the Soviets allowed the German army to train on Soviet territory to evade the restrictions of the Treaty of Versailles, and the fact that German and Soviet intelligence and espionage services began cooperating and sharing information as early as 1937. Stalin's sine qua non for an alliance with Britain and France was that Poland give the Red Army transit rights across Polish territory to engage the German Army, and he knew very well that that was a condition that the Polish government could never agree to. This reluctance by the Polish government to allow Soviet troops into their territory, far from being the obstinate ineptitude that Shirer portrays it as, was entirely rational. The Poles were in an impossible situation in 1938 and 1939. Their only legitimate hope to defend against German aggression was to get help from the Soviets, but they knew that Soviet help would inevitably mean Soviet domination. Shirer never mentions that the Red Army was at the gates of Warsaw during the Soviet-Polish war of 1919-1921 (Stalin was one of its commanders during that war) and that only a miracle comparable to that of the Battle of the Marne prevented them from taking the city, nor does he acknowledge that the Soviet domination that the Poles feared actually happened after World War II. And remember that almost half of inter-war Poland was territory formerly belonging to the Russian Empire. The Polish government knew that their position was impossible, and they chose to deal with their predicament with dignity: they refused to cave in to German bullying, and they refused to hand their country over voluntarily to the Soviets. It was stubbornness, I suppose, but it was a noble stubbornness, regardless of what Shirer says. An alliance with Stalin would have meant British and French complicity in Soviet aggression against Poland, Romania, Estonia, Latvia, and Lithuania. It was one thing for Britain to agree to this when it was a fait accompli, as it was by the time of the Yalta conference in 1945. It was quite another for them to do so in 1939. A British government that agreed to such an alliance would have fallen, and it would have deserved to do so.
Shirer's basic problem is that he doesn't regard Stalin and the Soviet regime as being evils on the same plane as Hitler and the Nazi regime. It doesn't make a whole lot of sense to try to determine which was the more evil, but it is unquestionable that both were directly responsible for the intentional infliction of huge amounts of death and human suffering. It is perfectly natural that any government not evil would have shrunk in the late 1930s from allying with either regime, and Shirer's refusal to understand that renders him obnoxious and his book tendentious.
(I am too lazy to quote from The Rise and Fall of the Third Reich in support of my arguments, but see the chapters "The Turn of Poland" and "The Nazi-Soviet Pact".)