After the creation of the Soviet Union, there was a basic conflict over how to rebuilt the Soviet economy.
On the one side, there was Lenin who believed in his New Economic Policy. This policy was one that was somewhat more capitalistic than might be expected. Lenin wanted small farmers and manufacturers to be able to participate in an open market while keeping larger concerns under governmental control.
On the other side were those who opposed the NEP. These were people like Trotsky who wanted the country to industrialize very rapidly. They wanted to abandon the NEP and change the economy more radically than Lenin wanted to.
Stalin resolved this debate in favor of Trotsky's ideas. He pushed for extremely rapid industrialization.