Stalin's government posed a threat to the Russian people directly for the simple fact that he was a mass murderer and many of them were in his crosshairs. Stalin ordered the deaths of almost 20 million of his own people during his rule, and sent millions of others to hard labor in a system of concentration camps known as Gulags. He ruled with a iron fist and killed or arrested anyone who might be a threat or who stood in the way of his plans.
His threat to the world was that he was expansionist, arming revolutionary movements in Europe and Asia and helping to start wars there. After 1949, the Soviet Union was also armed with nuclear weapons.
stalin's government posed a threat in such a way that europe could have being communist,I can say quarter of it was turned into communist states for several years.Stalin in his rule he introduced poltical policies that aimed at removing his opponets for example leon Trotsky was assassinated during the years that the purges.The system was feared by many people who stood against him,in 1924 stalin killed all the rich peasants(kulaks) that opposed his idea of collectivisation.