What was the reason behind Stalin's rise to power?

There are many reasons behind Stalin's rise to power. After the death of Vladimir Lenin in 1924, there was a power vacuum created with in the Communist Party. Many people believed that the natural heir to the leadership would be the leader of the Red Army, Leon Trotsky due to his close proximity to Lenin. The other favourite was Nikolai Bukharin, then editor of Party newspaper Pravda. However, it was Stalin who came out on top, his position of General Secretary allowed him to control appointments to the Party, and his previous holdings of Rabkrin allowed him to communicate better with the grassroots members of the Party.