On August 18, 1917, the top Bolshevik leader, Vladimir Lenin, set up a political bureau – known first as Narrow composition and, after October 23, 1917, as Political bureau – specifically to direct the October Revolution, with only seven members (Lenin, Trotsky, Zinoviev, Kamenev, Stalin, Sokolnikov, and Bubnov), but this precursor did not outlast the event; the Central Committee continued with the political functions. However, due to practical reasons, usually fewer than half of the members attended the regular Central Committee meetings during this time, even though they decided all key questions.
The 8th Congress of the 8th Party Congress in 1919 formalized this reality and re-established what would later on become the true center of political power in the Soviet Union. It ordered the Central Committee to appoint a five-member Politburo to decide on questions too urgent to await full Central Committee deliberation. The original members of the Politburo were Lenin, Leon Trotsky, Joseph Stalin, Lev Kamenev and Nikolai Krestinsky.
The Stalinist system was based upon the system conceived by Vladimir Lenin, often referred to as Leninism. Certain historians and political scientists credit Lenin for the evolution of the Soviet political system after his death. Others, such as Leonard Schapiro, argue that the system itself, from 1921, evolved an inner-party democratic system to a monolithic one in 1921, with the establishment of the Control Commission, the ban on factions and the ability given to the Central Committee to expel members they deemed unqualified. These rules were implemented to strengthen party discipline, however, the party continued under Lenin and the early post-Lenin years to try to establish democratic procedures within the party. For instance, by 1929, leading party members began criticizing the party apparatus, represented by the Secretariat headed by Stalin, of having too much control over personnel decisions. Lenin addressed such posing questions in 1923, in his articles "How We Should Reorganize the Workers' and Peasants' Inspectorate" and "Better Fewer But Better". In these, Lenin wrote of his plan to turn the combined meetings of the Central Committee and the Control Commission into the party's "parliament". The combined meetings of these two would hold the Politburo responsible, while at the same time guard the Politburo from factionalism. Admitting that organizational barriers may be inadequate to safeguard the party from one-man dictatorship, Lenin recognized the importance of individuals. His testament tried to solve this crisis by reducing both Stalin's and Leon Trotsky's powers.
While some of his contemporaries accused Lenin of creating a one-man dictatorship within the party, Lenin countered, stating that he, like any other, could only implement policies by persuading the party. This happened on several occasions, such as in 1918 when he threatened to leave the party if the party did not go along with the October Revolution, or persuading the party to sign the Treaty of Brest-Litovsk, or the introduction of the New Economic Policy (NEP). Lenin, a noted factionalist before the Bolshevik seizure of power, supported the promotion of people he had previously clashed with on important issues to the Politburo; Trotsky and Lenin had had several years of violent polemics between them, while Grigori Zinoviev and Lev Kamenev both opposed the Central Committee resolution which initiated the October Revolution.
From 1917 to the mid-1920s, congresses were held annually, the Central Committee was convened at least once a month and the Politburo met once a week. With Joseph Stalin's consolidation of power, the frequency of formal meetings declined. By the mid-1930s, the Central Committee began meeting only once a month, and the Politburo convened at most once every third week. The Politburo was established, and worked within the framework of democratic centralism (that is a system in which higher bodies are responsible to lower bodies and where every member is subordinate to party decisions). The nature of democratic centralism had changed by 1929, and the freedom of expression which had been previously tolerated within the party, was replaced with monolithic unity. The main reason being Stalin's defeat of the opposition; the Left Opposition, the Right Opposition etc. It is generally believed that under Stalin the Politburo's powers were reduced vis-a-vis Stalin.