In Lenin’s last testament he commented on the men, and wrote who he thought should become the next leader. Lenin said about Stalin that he had "unlimited authority concentrated in his hands" and suggested that "comrades think about a way of removing Stalin from that post." Stalin was the General Secretary of the Party. Lenin also said that he “is too rude and this defect”. Lenin suggested that Bukharin was the more suitable candidate.
Stalin persuaded the Central Committee to get rid of this document to prevent people from finding out that Lenin did not want Stalin as leader. This showed Stalin in a bad light.
Although Kamenev and Zionoviev agreed with Trotsky politically they very much disliked him personally and so they formed an alliance with Stalin to prevent him coming to power. They also doubted his loyalty due to the fact that he only joined the Bolsheviks in 1917 where as Stalin had been a member for over 20 years.
Stalin had a fairly weak position in the party as the General Secretary he was able to use this position to gain popularity. Being General Secretary meant that Stalin was able to allocate important jobs to his close supporters, and ensure that none were given to anyone likely to oppose him. In fact he was even able to drive out opponents, likely to support Trotsky.
Stalin, being very clever was able to play off the left and right wing groups of the Communist Party causing them to turn against each other. For example, he played off the right-wing party members, Kamenev and Zinoviev, using their fear of right wing members such as Trotsky, and international communism to persuade them to form an alliance with him. Stalin, Kamenev and Zinoviev worked together to remove Trotsky as Commissar For War as they thought this made him too powerful. He was also able to use his wit, along with the misfortune of others, to deceive the public into believing that he was the rightful heir to Lenin. An example of this is when Lenin died in 1924. Fortunately for Stalin, Trotsky fell ill at this point, and Stalin was left to arrange the funeral, and appear as Lenin’s chief mourner in front of thousands. The touching service given by Stalin enabled him to keep the thousands of witnesses, and many more under the illusion that he was Lenin’s faithful disciple.
Stalin believed in ‘Socialism in One Country’ he proposed that Russia should establish Communism long-term. Where as Trotsky believe in a ‘Permanent Revolution’ he thought that they should spread the revolution to other countries in Europe. Stalin idea was very popular with the right winged members as they thought it was an achievable goal. The idea of a ‘Permanent Revolution’ was not as popular. He and others in the Politburo wanted to collectivise and industrialise the farms to boost agriculture. This would mean ending the NEP (New Economic Policy) that was introduced by Lenin. Stalin however said that they should follow the NEP, Stalin ended up collectivising the farms when he got into power anyway. Trotsky desperately wanted to boost other revolutionary movements in other countries; he would fund them and send agents out to help them. Although these ideas where supported by left wing members they were extremely unpopular with right winged members such as Kamenev, Zinoviev and Stalin.
So far Stalin had needed to use Kamenev and Zinoviev to out-manoeuvre Trotsky but by 1927 he had enough support from the Politburo that he did not need them anymore, they were expelled from the party along with Trotsky.
By 1929 Stalin had a clear majority of support in the Politburo. He now decided to back collectivisation. Bukharin opposed this but he was forced to resign. Stalin had now gained power in Russia. I believe that this was largely due to Stalin’s cunning plans to deceive the public into thinking he was the rightful heir to Lenin. He was also very clever in the fact that he turned others against each other. He also used his position in the party to great effect to remove any opposition to his race into power in 1929.