Due to the following factors Stalin was able to rise to power in 1929
Political scheming
Mistakes of his opponents
His power base, took up positions that he could use to put his own supporters into important posts and transfer supporters of his opponents to remote posts.
Played opponents against each other, (e.g. he took Bukharin’s side in the debate on the NEP to get rid of Trotsky and when that was done, he opposed Bukharin using Trotsky’s arguments).
Trotsky’s Flaws
The opponent’s underestimation of Stalin
His “appeared” relation and association with Lenin. (Especially seen at Lenin’s funeral)
Stalin was a very cunning & clever politician and planned carefully
He associated himself with Lenin wherever possible
His positions in the Communist Party
Trotsky’s brilliance worked against him
His many flaws
The other Politburo members underestimated Stalin
Stalin used the disagreements to his own advantage
Stalin was able to appeal to the people
Trotsky’s flaws played a large part in allow Stalin to take rule over the USSR
Trotsky was arrogant and often offended party members
Failed to take the opposition seriously
Made little effort to build up any support in the ranks of the party
Seriously underestimated Stalin
Became sick later and was seen as weak and inactive
Did not directly address the people
He was Jewish and somewhat subject to anti-Semitism
Trotsky was more concerned about international affairs rather than national affairs, which frightened people… thinking that Trotsky would involve Russia in bad international affairs and that he would not do much about their own problems.
Tricked into not going to the funeral.
Stalin’s Positions in the party
People’s Commissar for Nationalities (1917)
In this post, Stalin was in charge of the officials in the various republics outside Russia.
Liaison Officer between the Politburo and the Orgburo (1919)
This post, allowed Stalin to monitor party personnel and policy.
Head of the Worker’s and Peasants’ Inspectorate (1919)
General Secretary of the Party (1922)
Stalin played one side against the other to take power:
First, he allied with Zinoviev and Kamenev to cover up Lenin’s Will and to get Trotsky dismissed (1925). Trotsky went into exile (1928).
Then, he advocated ‘Socialism in one country’ (he said that the USSR should first become strong, then try to bring world revolution) and allied with the Rightists to get Zinoviev and Kamenev dismissed (1927). Stalin put his supporters into the Politburo.
Finally, he argued that the NEP was uncommunist, and got Bukharin, Rykov and Tomsky dismissed (1929).
