Few would doubt Stalin was a strong and effective politician and that that this led to his leadership. How much of this power was due to the mistakes of those who surrounded him rather than Stalin's own ability or luck or the circumstances and structure of power?
After Lenin died a collective leadership was introduced: the politburo. At this time Stalin was described as a gray blur opposed to people like Trotsky a charismatic and clever orator. Trotsky's first mistake was not seizing power shortly after Lenin's death when he was at his most powerful. Likewise long standing prominent Bolsheviks such as Zinoviev and Kamenev failed to become sole leader seemingly happy to share power. Thus giving Stalin the opportunity to gain more power for himself. Was this underestimation of Stalin by his opponents a shortsighted mistake or rather Stalin's well-played strategy? Stalin's opponents failed to seize power when they had the chance.
They made the mistake of overestimating Trotsky keeping Stalin as an ally against him.
Trotsky the obvious successor to Lenin seemed unwilling to gain a strong power base in the party. This was one of his many mistakes. He was generally feared or mistrusted by other leaders within the party who saw him as a threat. He was seen as a Napoleonic figure that might seize power for himself. He didn't help himself by not turning up to Lenin's funeral for instance. However this mistake might again have been Stalin's able strategy as Trotsky maintained Stalin had given him the wrong date (Although a dubious excuse in my opinion). Trotsky seemed to believe the struggle for personal power was beneath him. Was this an actual mistake or was his failure to clasp power inevitable due to failing health political history etc. Later on in order to...