The Defeat of Trotsky
After Lenin's death Trotsky was the most obvious successor. This fact was his weakness.
Trotsky was the Commissar of War, and the creator of the Red Army. This concerned many as Trotsky was an ambitious man, and many feared he would use the Red Army to seize power.
Trotsky believed in Worldwide Revolution, which Stalin countered with the policy of Socialism in One Country. Zinoviev and Kamenev therefore turned to Stalin and formed a Triumvirate to stop Trotsky.
Trotsky was an Ex-Menshevik which also weakened him.
He attacked Zinoviev and Kamenev in his 'Lessons of October', in which he drew attention to their lack of support for the revolution.
Trotsky frequently disagreed with Lenin. He was accused of inventing 'Trotskyism', a rival ideology to Leninism.
Trotsky was accused of Factionalism. At the meeting of the Central Committee in January 1925 he was condemned. He resigned as Commissar of War, the position that had given him continuing control of the army.
Stalin also damaged Trotsky's leadership bid. Trotsky was recovering from malaria in the Crimea when Lenin died and Stalin told Trotsky the wrong date of the funeral; by the time Trotsky realised, it was too late for him to travel back in time. This disrespect for Lenin damaged Trotsky's public image further.
The defeat of Zinoviev, Kamenev and the Untied Opposition
After Trotsky's defeat, Zinoviev and Kamenev became concerned that Stalin was the most powerful figure in the party.
Stalin now turned on them and Kamenev lost control of the Moscow Party. Zinoviev held on in Leningrad and launched an attack on the party policy of the NEP, arguing that it was Capitalist and that the time had come to introduce rapid industrialisation. They also started questioning…