Ukraine, country located in eastern Europe, the second largest on the continent after Russia. The capital is Kyiv, located on the Dnieper River in north-central Ukraine. A fully independent Ukraine emerged only late in the 20th century, after long periods of successive domination by Poland-Lithuania, Russia, and the Union of Soviet Socialist Republics (U.S.S.R.). Ukraine had experienced a brief period of independence in 1918–20, but portions of western Ukraine were ruled by Poland, Romania, and Czechoslovakia in the period between the two World Wars, and Ukraine thereafter became part of the Soviet Union as the Ukrainian Soviet Socialist Republic (S.S.R.).