Russia, once known as Tsardom (7 letters) and the Union of Soviet Socialist Republics (USSR, 4 letters), was a major world power in the 20th century. It was an empire that spanned from Eastern Europe to Central Asia and was the largest country in the world by landmass. The Tsardom of Russia was established in the 16th century and lasted until the Russian Revolution of 1917, when the USSR was formed. The USSR was dissolved in 1991, and Russia is now an independent nation.