Until now, the history of the USSR was only described, but no one tried to explain it. In this work, using the methods of political economic analysis, the logic of the development of our country in the twentieth century is revealed. The materialistic approach to explaining the historical process made it possible to identify the fundamental factor that determined the development of the Soviet Union throughout the entire period of its existence. As a result, all stages and facts of the history of the USSR received their logical explanation.