An excerpt from a longer answer:Significant economic and political changes took place in 1921, that altered the trajectory of the Communist Party. The New Economic Policy (NEP) sought to bring order after War Communism, implementing quasi-capitalist features. The 10th Party Congress challenged opposition within the party. Whilst both played a significant role in perpetuating Stalin’s domination of the Communist party, other factors, such as terror and the position of General Secretary, must also be seen as contributing to political entrenchment. The NEP allowed Stalin to limit opposition within his party. By 1928, the leader’s position was secure, having successfully outmanoeuvred both left and right opposition. Much of this can attributed to the NEP. Its capitalist features, such as productivity bonuses, incentives and the legalisation of private profiteering, created divisions within the party. Whilst some thought it an ideological retreat, others deemed such actions essential to save the economy. It was these divisions that Stalin was able to exploit. Leon Trotsky was the greatest challenge to his securing of power and, in response to accusations of undermining the Leninist state following calls for the implementation of a command economy, Stalin successfully removed the Left in 1926. By 1928, Stalin had a secure position as leader of the party. The changes of 1921 explain Stalin’s increasing domination over the Communist party because they facilitated the removal of opposition in a means deemed ‘justifiable’. As a result, the leader was able to surround himself with loyalists over which he had considerable control. Thus, potential opposition to policies such as the Five-Year-Plan was avoided and further changes could be made. The NEP was significant in facilitating Stalin’s increasing power because it justified the removal of key opponents and fostered party loyal supporters. The 10th Party Congress of 1921 was another critical political change that contributed to Stalin’s increasing domination. It saw the implementation of ‘On-Party-Unity’, banning the formation of factions. As with the NEP, this measure significantly reduced potential opposition. Criticisms filed against the Five-Year Plans, such as over ambitious targets or over-zealous implementation, were prohibited from becoming factional divides as a result of this policy, and any challenges were expressed in an individual capacity. The prevention of factions allowed Stalin to foster a secure and loyal powerbase, allowing the leader much greater personal control and authority. Stalin used this policy to remove opposition towards the NEP. The Left were accused of forming factions in 1926, a time when Stalin himself had reduced personal power. Such a political manoeuvre also allowed him to justify the Leninist state. Without the removal of this opposition prior to 2918, Stalin would have been incapable of increasing his domination. The ban on factions implemented in 1921 was therefore significant in increasing Stalin’s domination of the Communist Party between 1928 and 1933 because it secured his position, removed any chance of opposition and allowed him to justify his actions.