In 1917 the Social Democratic Workers' Party (Bolsheviks) had 200,000 members. The following year, Vladimir Lenin persuaded members to change the name of the organization to the Communist Party of the Soviet Union (CPSU) .
Traditionally, the Party Congress elected a 27 member Central Committee every year. Lenin decided this was too large to determine policy and in 1919 the party created a Politburo. This was made up of five members (increased to nine in 1925 and ten in 1930). Its first members were Vladimir Lenin, Leon Trotsky, Joseph Stalin, Lev Kamenev and Nikolai Krestinsky.
There were over 700,000 members of the CPSU in 1921. At first the Politburo allowed free and open debate at party meetings. However, as a result of the Civil War, this policy changed. At the Party Congress in 1921 all factions such as the Workers' Opposition were banned. The following year all political parties other than the CPSU were closed down.
The CPSU was now all powerful. It controlled the government, which consisted of the Council of People's Commissars, headed by its chairman (who was prime minister). The CPSU also appointed all local and national public officials, who had to be members of the party before they could be appointed to these posts.
Gradually power passed from the Politburo to the General Secretary, who controlled the appointment of party members to key jobs throughout the country. Joseph Stalin, who became General Secretary in April, 1922, dominated the CPSU after the death of Vladimir Lenin in January, 1924.
In the 1930s Joseph Stalin instigated a series of purges against senior members of the CPSU. This included the removal of Leon Trotsky, Lev Kamenev, Gregory Zinoviev, Ivan Smirnov, Nikolai Yezhov, Nickolai Bukharin, Alexei Rykov, Genrikh Yagoda, Gregory Ordzhonikidze, Vladimir Antonov-Ovseenko, Nikolai Krestinsky and Christian Rakovsky from power. These men were either executed, assassinated, committed suicide, or died in labour camps.