The area currently known as Turkmenistan has long served as a thoroughfare for many other nations and cultures. Merv is one of the oldest oasis-cities in Central Asia and was once the biggest city in the world. In medieval times, Merv was also one of the great cities of the Islamic world and an important stop on the Silk Road. Annexed by the Russian Empire in 1881, Turkmenistan later figured prominently in the anti-Bolshevik movement in Central Asia. In 1925, Turkmenistan became a constituent republic of the Soviet Union, the Turkmen Soviet Socialist Republic (Turkmen SSR); it became independent after the dissolution of the Soviet Union in 1991.