The Communist Party was continually purged in the 1930s after the Ryutin Affair and the murder of Kirov.
1938 was the peak year for purges where a fifth of the Communist Party was expelled and many thousands shot.
Old Bolsheviks were considered to be people who had joined the party before 1924 and could therefore remember a time when Stalin was not an all powerful dictator.
Thousands of Old Bolsheviks were arrested and executed, particularly after the show trials of Zinoviev and Kamenev.
It is estimated that less than 10% of the party membership in 1939 had joined the Party before 1920.
Delegates to the 1934 Party Congress suffered from the purges because Kirov gained more votes for the Politburo than Stalin did.
Stalin fixed the result so that he and Kirov gained the same amount of nominations.
Stalin never forgot his perceived humiliation in 1934 and when the Terror was in full swing, delegates who attended the Party Congress that year were in particular danger.
1,108 of the 1,966 delegates had been arrested by 1939.
The Terror concentrated the minds of leading Communists that loyalty to Stalin was the best way to stay in power.
The Politburo were full of Stalin's cronies after 1929 and were unwavering in his support.
President of the USSR Kalinin never asked for the release of his wife who was imprisoned in a gulag between 1938 and 1945.
Molotov who was Stalin's closest ally stopped pleading the case of his wife who was also imprisoned.
Molotov's daughter declared that she had no mother on her application to join the party.
Sergo Ordzhonikidze was a member of the Politburo who opposed the excesses of the NKVD.
After a heated row with Stalin, Sergo committed suicide in February 1937.
He was given a state funeral and his death was officially declared as a heart attack.
He was the last leading Communist to oppose Stalin's policies.
There were about 2.5 million party members in 1935 but by 1939, this had fallen to around 1.5 million as a result of the arrest of over a million party members and 600,000 executions.
New members were recruited to the party in the late 1930s.
These tended to be younger and better educated than pre-1930 recruits partly because Stalin was concerned with operating the Five Year Plans more effectively.
Stalin and the Politburo were very concerned with the amount of resistance to their policies of industrialisation and collectivisation among regional party officials.
Part of the focus of the Terror was to bring much closer central control over regional party organisations.
In Georgia, 2 state prime ministers, 4 out of 5 of the regional party secretaries and thousands of lesser officials lost their posts.