One of the main policies of the Stalinist era was Rapid Industrialization. This was partially because industrialization was necessary to justify the Bolsheviks remaining in power in the Soviet Union. According to Marxism, the "Dictatorship of the Proletariat" was supposed to take place after the capitalist period, and capitalism meant, among other things, industrialization (in order to increase production capacity). Since Russia was mainly rural and agrarian when the Bolsheviks took power and introduced the "Dictatorship of the Proletariat", rapid industrialization was ideologically necessary to move through and past the capitalist phase into socialism.

Another reason for rapid industrialization was the military. The Russo-Japanese War and WWI painfully demonstrated that Russia had lagged behind its neighbors militarily, and both Russian history and the building of socialism in one country meant (by definition) that the Soviet Union was surrounded by (non-socialist) enemies who could attack at any time. This was not simply an abstract concern, of course: the Soviet Union was invaded by Nazi Germany in 1941 and as many as 29 million people died. We will look at WWII next class.

Learn more about Stalin and the Drive to Industrialize the Soviet Union here: http://www.inquiriesjournal.com/articles/1684/stalin-and-the-drive-to-industrialize-the-soviet-union

To finance industrialization, and to deal with a (potential) political threat from the peasantry (esp. in Ukraine), Stalin moved the peasants into collective farms, which was basically a reintroduction of serfdom. This policy (Collectivization) led to the death of millions by execution, starvation, and privation.

There is reason to believe that Stalin ultimately became concerned about a political backlash because of this policy, and that is one of the reasons he initiated "The Purges" - a "cleansing" of the Communist Party, and ultimately the country, of all real, perceived, and potential enemies. This resulted in millions more deaths.

Learn more about the Stalinist purges and the Gulag: USSR_Stalin_Great_Purge.pdf (Source)