Present-day Turkmenistan covers territory that has been at the crossroads of civilizations for centuries. The area was ruled in antiquity by various Persian empires, and was conquered by Alexander the Great, Muslim armies, the Mongols, Turkic warriors, and eventually the Russians. In medieval times, Merv (located in present-day Mary province) was one of the great cities of the Islamic world and an important stop on the Silk Road. Annexed by Russia in the late 1800s, Turkmenistan later figured prominently in the anti-Bolshevik movement in Central Asia. In 1924, Turkmenistan became a Soviet republic; it achieved independence upon the dissolution of the USSR in 1991. Extensive hydrocarbon/natural gas reserves, which have yet to be fully exploited, have begun to transform the country. In 2010, new gas export pipelines that carry Turkmenistani gas to China and to northern Iran began operating, effectively ending the Russian monopoly on Turkmenistani gas exports. In 2016 and 2017, Turkmenistani sales of natural gas were halted to Russia and Iran, respectively, making China the sole major buyer of Turkmenistani gas. As of April 2019, there are plans to renew gas exports to Russia. President for Life Saparmyrat NYYAZOW died in December 2006, and Gurbanguly BERDIMUHAMEDOW, a deputy chairman under NYYAZOW, emerged as the country's new president. BERDIMUHAMEDOW won Turkmenistan's first multi-candidate presidential election in February 2007, and again in 2012 and in 2017 with over 97% of the vote in both instances, in elections widely regarded as undemocratic.