On the basis of a secret clause of the Molotov–Ribbentrop Pact, the Soviet Union invaded Poland on September 17, 1939, capturing the eastern provinces of the Second Polish Republic. Lwów (present-day Lviv), the capital of the Lwów Voivodeship and the principal city and cultural center of the region of Galicia, was captured and occupied by September 22, 1939 along with other provincial capitals including Tarnopol, Brześć, Stanisławów, Łuck, and Wilno to the north. The eastern provinces of interwar Poland were inhabited by an ethnically mixed population, with ethnic Poles as well as Polish Jews dominant in the cities. These lands now form the backbone of modern Western Ukraine and West Belarus.