But Stalin's grip on power was not shaken, save perhaps in his home, where his wife Nadezhda committed suicide in 1932.
Then, in December 1934, Stalin ordered the assassination of Sergei Kirov, a member of his Politburo whom he suspected being a locus of opposition to his rule. This touched off the "Great Terror," a period during which Stalin had all of his enemies, real and imagined, put to death or shipped off to Siberian prisons. This period culminated in the Moscow Show Trials of 1936-38; in these, Stalin tried all of his defeated 1920s opponents for treason--and, via horribly effective torture, forced them to make public confessions which he broadcast worldwide.
Meanwhile, World War II was fast approaching. As Hitler rose to power in Germany, Stalin first contemplated forming a defensive alliance with Britain and France against the Nazis. But he wanted to avoid war at all costs, and in 1939 he signed the Nazi- Soviet Pact, which pledged that the two dictatorships would not attack one another, and granted Stalin permission to take over the Baltic States and eastern Poland, and prosecute a war in Finland. But in June of 1941 Germany invaded the Soviet Union in blatant defiance of their pact. At first, the Red Army suffered catastrophic defeats, but they rallied, and after crushing the Nazis at Stalingrad in 1942-43, they were on their way to winning the war.
As victory inched nearer, Stalin seemed determined to make the Soviet Union dominant in Europe. Even during the war, he made inflexible demands of his new allies, Prime Minister Winston Churchill of Britain and President Franklin Roosevelt of the United States. After Germany fell, he used Red Army troops to forcibly install Communist governments in Eastern Europe and further his country's interests around the world. Meanwhile, he launched a new wave of repression in the Soviet Union. By 1949, Soviet scientists had exploded an atomic bomb, giving them nuclear parity with the United States.