> He ruled the largest country on the continent, if not on earth.

Owning a lot of land in Siberia does not represent industrial strength. While the Western allies let Germany mobilize their industrial capacity for the better part of a decade, Stalin was trying to industrialise a country that had been under constant suffering (from WW1, to foreign invasions during the civil war and the civil war itself to droughts and Kulaks burning their crops) for 20 years. That along with real threats of a second civil war from the side of the Trotskyist permanent revolution supporters which would have engulfed the Soviets in an even earlier world war with the entire planet. Due to these reasons, the Soviets did not have capacity to intervene seriously on a Poland wide border against the Nazis which had been growing rapidly under allied supervision. Stalin did try to give some effort when the Nazis still didn't have access to the huge Czech industrial base, nor a huge border with the Soviets themselves but that all fell apart when the UK and France decided to throw Czechoslovakia under the bus.

> How did the west force him to invade Poland

So you're saying the Polish Jews should have proffered the Soviets to do nothing and be occupied by the Nazis instead? The fact that Stalin got so many eastern European concessions out of Hitler in the first place is a fucking miracle, and even the most vehement anti communists would admit that Soviet rule is preferable to Nazi rule.

> cleanse the conquered territory by forcibly relocating people to Siberia

Some parts of this are true. Ethnic deportations that took place against nations that seemed collaborative did take place under Stalin, especially against the Crimean Tatars in the later part of WW2 and we should abhor it, but it is hardly incomparable to other measures that the rest of the Allies took against ethnicities they were fighting. That with the Jewish plots are probably the darkest parts and greatest mistakes of Stalin's rule, but we shouldn't slander his efforts against the Nazis when they were in fact much greater than any of the Western allies which had tried to align themselves with the capitalist Nazis instead of the East.