Why did Stalin become leader of the USSR?
Lenin, the leader of Russia died from ill health in 1924, without choosing a successor, but how did Stalin, one of the least likely people to take over become leader of the Ussr?
His role as General Secretary was used by Stalin to great advantage. It allowed him to see all important documents flowing in and out of the party. This fortunate for Stalin, included Lenin's last testament, which stated Lenin's desire for a dictatorship of the party as well as the fact that Stalin should not rule. His role also allowed him to recruit people who were loyal to him, remove members who weren't and also to collect information on every party member.
After Lenin's death he waited, allowing other Politburo members to state their preferred policies - he then ganged up on groups of them, using his alliances and his party contacts to destroy the opposition. His did this twice in the 1920s, destroying Trotsky and his supporters and Zinoviev and Kamenev and their supporters.
Stalin's character in the role also helped him to degrade other candidate's reputations. This can be seen when Stain tells Trotsky the wrong date for Lenin's funeral. He also changed his allegiance. At first he disagrees with the idea of NEP to disagree with Trotsky but later opts for it.
He became the disputed leader of the USSR in 1928. Once he was the undisputed leader - the Vozhd he continued to use the position of General Secretary of the Communist Part to promote loyal supporters and demote, or expel from the party those who he could not be sure about. From the mid 1930s began to use show trials - public events where the accused had to follow a script, nearly always ending in a guilty verdict, and purges - expelling great numbers from the party and arresting people arbitrarily. Fear became one of the main weapons Stalin used against the Soviet people. Stalin also bugged the offices of the other members of the Politburo and collected information...