What was joseph stalins role in WWII

During World War II Stalin emerged, after an unpromising start, as the most successful of the supreme leaders thrown up by the belligerent nations. In August 1939, after first attempting to form an anti-Hitler alliance with the Western powers, he concluded a pact with Hitler, which encouraged the German dictator to attack Poland and begin World War II. Anxious to strengthen his western frontiers while his new but palpably treacherous German ally was still engaged in the West, Stalin annexed eastern Poland, Estonia, Latvia, Lithuania, and parts of Romania; he also attacked Finland and extorted territorial concessions. In May 1941 Stalin recognized the growing danger of German attack on the Soviet Union by appointing himself chairman of the Council of People’s Commissars (head of the government); it was his first governmental office since 1923.