Though Germany was technically Russia’s ally, Soviet leader Joseph Stalin had no delusions that they were friends. Instead, he used this time to build up his forces for what he saw as an inevitable invasion.

First, on the heels of the German invasion of Poland in September 1939, Stalin had his troops invade and reclaim the land Russia had lost in World War I. Next he turned his attention to Finland, which was only 100 miles from the newly named Leningrad. He initially tried to negotiate with the Finnish government for some sort of treaty of mutual support. When this failed he simply invaded. While the giant Russian army ultimately won, the fact that little Finland held them off for three months demonstrated how poorly organized the bigger force was.

Initially, Stalin believed he had several years to build up his army before Germany would invade, figuring it would take the Germans at least that long to conquer France and Britain. However, when France fell quickly in 1940, it seemed he might have miscalculated, so he again sent Molotov to Berlin to stall for time. Meanwhile, Hitler trained his sights on Britain, turning his attention to destroying the Royal Air Force as a prerequisite for the invasion of Britain.

What Stalin did not realize was that Hitler had simply overstretched himself in Yugoslavia and planned to delay the invasion by only a few weeks. Hitler aimed to destroy Stalin’s Communist regime, but he also hoped to gain access to resources in Russia, particularly oil. Throughout the first half of 1941, Germany dug in to safeguard against an Allied invasion of Western Europe as it began to mobilize millions of troops to invade the Soviet Union. Stalin even refused to believe the report of a German defector who claimed that the troops were massing on the Soviet border at that very moment.