Soviet annexation of Western Ukraine, 1939–1940

On the basis of a secret clause of the Molotov–Ribbentrop Pact, the Soviet Union invaded Poland on September 17, 1939, capturing the eastern borderland provinces of Poland with little opposition. Lwów, present day Lviv, the principal city and cultural center of the region of Galicia, was captured and occupied by September 22. These provinces were inhabited by an ethnically mixed population, with ethnic Ukrainians dominant in rural areas, and Poles dominant in the cities. They now form the backbone of modern Western Ukraine.