The most fundamental proximity of the two regimes, in my view, is not ideological but geographical. Given that the Nazis and the Stalinists tended to kill in the same places, in the lands between Berlin and Moscow, and given that they were, at different times, rivals, allies, and enemies, we must take seriously the possibility that some of the death and destruction wrought in the lands between was their mutual responsibility. What can we make of the fact, for example, that the lands that suffered most during the war were those occupied not once or twice but three times: by the Soviets in 1939, the Germans in 1941, and the Soviets again in 1944?
Like any incredibly successful politician, Stalin was lucky. He was lucky that Lenin died when he did, because otherwise Trotsky's position in the Soviet state would have become so strong as to withstand his attack. He was lucky, too, that he was not ousted immediately after Lenin's death, as Lenin's Testament had advised. But he also showed an amazing ability to play his opponents off one another until he was powerful enough to stand on his own: first, he allied with the "Leftists," Zinoviev and Kamenev to diminish Trotsky's power; then, with Trotsky's star in eclipse, he turned on the "Leftists," forming an alliance with Bukharin and the other "Rightists" to defeat Zinoviev and Kamenev and drive them out of the Communist Party. All the while, Stalin was building up his own base of support, so that within a year of the elimination of the "Leftists" he was ready to challenge, and defeat, Bukharin and take over supreme power himself. His enemies failed because they never understood that his motivations were different from theirs--while they cared about principles and policy, all that mattered to Stalin was power.