What tatic did Joseph Stalin use to intimidate and punish opponents of the soviet union

Stalin is one of the ruthless dictators of the 20th century. He used the method of repression where he would execute majority of people he thought were against the regime. He also deported over million of people, mostly men, to Goulags which were working camps in the middle of Siberia. Since the conditions in these camps were inhuman, most of the prisioners would die of cold and hunger. They say escaping these camps was almost impossible.