What reasons can you give to explain how Stalin was able to seize power in the USSR by 1928

Stalin, Joseph Vissarionovich, 1879-1953, Soviet Communist leader and head of the USSR from the death of V. I. Lenin (1924) until his own death, b. Gori, Georgia. His real name was Dzhugashvili (also spelled Dzugashvili or Djugashvili); he adopted the name Stalin (man of steel) about 1913. After the October Revolution of 1917, Stalin, already a member of the central committee since 1912 entered the Soviet cabinet as people's commissar for nationalities and began to emerge as a leader …

…their power was broken. <Tab/>In 1927, 75 other leading Communisst were expelled for opposing Stalin. No one could stop Stalin doing what he wanted because he had packed the Communist Party with his supporters. Finally, when there was no any strong and supportive by people persons, Stalin was left alone as the only candidate for the leadership of Russia. Completely, by 1928 Stalin had emerged as the sole leader of the Soviet Union.