Ukraine was the center of the first Slavic state in Eastern Europe. Known as Kievian Rus, the empire became the biggest and most powerful state in Europe during the 10th and 11th centuries. Eventually the empire was weakened by internal issues then conquered by the Mongol Empire in 1223. In the 14th Century, Kievian Rus was incorporated into the Grand Duchy of Lithuania and eventually into the Commonwealth of Poland and Lithuanian. In the 17th century the Ukrainians rebelled against Poland and gained independence for a period of around 100 years. In the 18th Century the country was conquered by Russia and was incorporated into the powerful Russian state.  When Tsar Nicholas II abdicated the throne in 1917, The Ukraine declared independence from Russia. However, in 1920, the area was re-conquered and forced to become part of the Soviet Union. During the early 1920's and the early 1930's, a large number of Ukrainian citizens suffered famines as a result of the Russian Civil War and the policies of Joseph Stalin. During the later famine, it is believed that over 7 million Ukrainians died. When World War II came along, the Germans captured large parts of the Ukraine and it is believed that another 8 million Ukrainians may have died as a result of the German invasion and the Soviet  re-conquering of the territory. Eventually, the Ukraine was able to achieve independence in 1991 when the Soviet Union was dissolved. However, democracy has remained elusive and the country has had a difficult time shaking off a history of state control and corruption. In 2004, the "Orange Revolution" forced the government to institute electoral reforms, allowing an internationally monitored vote which brought Viktor Yushchenko into power. Subsequent issues in the Yushchenko administration allowed his rival Viktor Yanukovych to be elected to parliament where he become prime minister in 2006.