 After the Soviet invasion of Poland ( beginning 17 September 1939 ) that followed the German invasion that had marked the start of World War II ( beginning 1 September 1939 ) , the Soviet Union annexed the eastern parts ( " <unk> " ) of the Second Polish Republic , comprising 201 @,@ 015 square kilometres ( 77 @,@ 612 sq mi ) and a population of 13 @.@ <unk> million . Hitler and Stalin shared the goal of <unk> Poland 's political and cultural life , so that Poland would , according to historian Niall Ferguson , " cease to exist not merely as a place , but also as an idea " . 
