The expulsion of Leon Trotsky from the Soviet Communist Party in 1927 represented a significant moment in the power dynamics of the Soviet leadership. Trotsky, a key figure in the Bolshevik Revolution and a leading theorist of Marxism, had been a prominent opponent of Stalin's policies. The split between Trotskyists and Stalinists highlighted deep ideological rifts within the Communist Party. Trotsky had argued for a continuous revolution that extended beyond the Soviet borders, while Stalin's 'socialism in one country' stance sought to establish a strong Soviet state first. The internal debates grew more intense as the political landscape of the Soviet Union began to harden and factions became more polarized.

The decision to expel Trotsky was made during the 15th Congress of the Soviet Communist Party as part of broader efforts by Stalin to eliminate rivals and consolidate power. The maneuvering behind the scenes included political machinations and alliances, with many former supporters of Trotsky shifting their loyalty to Stalin in fear of political retribution. This congress marked the culmination of this lengthy struggle, with Trotsky's expulsion effectively ensuring Stalin's control over the party and setting the stage for his totalitarian regime.

Following Trotsky's ousting, he became increasingly isolated within the party and the country, ultimately leading to his exile. He continued to criticize Stalin from abroad, but his influence diminished significantly as Stalin strengthened his grip on power. This event is crucial to understanding the trajectory of Soviet history, particularly in the context of Stalin's rise to dictatorial authority and the subsequent purges that would characterize his rule.