Outline and explain the main reasons why Stalin succeeded Lenin as leader of the USSR

The first reason is that Stalin wielded significant power and influence as General Secretary of the Party, having been appointed in 1922. Due to his position as an administrator he was both underestimated, described as a "grey blur", and held considerable power over the workings of the Party. Stalin's power of the patronage allowed him to appoint his own supporters to the Party and pack Congresses with loyal members.Secondly, when Lenin died in 1924, Stalin was in a position to present himself as Lenin's successor and organised Lenin's funeral. Stalin undermine his main leadership rival, Trotsky, by forming an alliance with members of the "leftwing" of the party, Zinoviev and Kamenev. After 1925 Stalin turned his attention against the "United Opposition" of Kamenev and Zinoviev, expelling them both from the Party in 1927. Having dealt with Trotsky and the leftwing, Stalin moved on to attack the "rightwing" members Bukharin, Rykov and Tomsky, removing Bukharin from the Central Committee and censuring the two other members. Stalin became the undisputed leader in 1929 having eliminated factions on both the left and right of the party by using his power of patronage as General Secretary and having been underestimated by his rivals.