Until the 20th century, the lands of modern-day Belarus belonged to several countries. These included the Principality of Polotsk, the Grand Duchy of Lithuania, the Polish–Lithuanian Commonwealth, and the Russian Empire. After the Russian Revolution, Belarus became part of the Soviet Union. It was renamed the Byelorussian Soviet Socialist Republic (BSSR). The borders of Belarus took their modern shape in 1939. Some lands of the Second Polish Republic were added into it after the Soviet invasion of Poland. The nation and its territory were devastated in World War II. Belarus lost about a third of its population and more than half of its economic resources. In 1945 the Belorussian SSR became a founding member of the United Nations, along with the Soviet Union and the Ukrainian SSR.