In the 12th century, Turkmen and other tribes overthrew the Seljuk Empire.[35] In the next century, the Mongols took over the more northern lands where the Turkmens had settled, scattering the Turkmens southward and contributing to the formation of new tribal groups.[35] The sixteenth and eighteenth centuries saw a series of splits and confederations among the nomadic Turkmen tribes, who remained staunchly independent and inspired fear in their neighbors.[35] By the 16th century, most of those tribes were under the nominal control of two sedentary Uzbek khanates, Khiva and Bukhoro.[35] Turkmen soldiers were an important element of the Uzbek militaries of this period.[35] In the 19th century, raids and rebellions by the Yomud Turkmen group resulted in that group's dispersal by the Uzbek rulers.[35] In 1855 the Turkmen tribe of Teke led by Gowshut-Khan defeated the invading army of the Khan of Khiva Muhammad Amin Khan[36] and in 1861 the invading Persian army of Nasreddin-Shah.[37] In the second half of the 19th century, northern Turkmens were the main military and political power in the Khanate of Khiva.[38][39] According to Paul R. Spickard, "Prior to the Russian conquest, the Turkmen were known and feared for their involvement in the Central Asian slave trade."[40][41] City of Çärjew in Russian Turkestan, 1890 Russian forces began occupying Turkmen territory late in the 19th century.[35] From their Caspian Sea base at Krasnovodsk (now Türkmenbaşy), the Russians eventually overcame the Uzbek khanates.[35] In 1879, the Russian forces were defeated by the Teke Turkmens during the first attempt to conquer the Ahal area of Turkmenistan.[42] However, in 1881, the last significant resistance in Turkmen territory was crushed at the Battle of Geok Tepe, and shortly thereafter Turkmenistan was annexed, together with adjoining Uzbek territory, into the Russian Empire.[35] In 1916, the Russian Empire's participation in World War I resonated in Turkmenistan, as an anticonscription revolt swept most of Russian Central Asia.[35] Although the Russian Revolution of 1917 had little direct impact, in the 1920s Turkmen forces joined Kazakhs, Kyrgyz, and Uzbeks in the so-called Basmachi rebellion against the rule of the newly formed Soviet Union.[35] In 1921 the tsarist province of Transcaspia (Russian: Закаспийская область, 'Transcaspian Oblast') was renamed Turkmen Oblast (Russian: Туркменская область), and in 1924, the Turkmen Soviet Socialist Republic was formed from it.[35][43] By the late 1930s, Soviet reorganization of agriculture had destroyed what remained of the nomadic lifestyle in Turkmenistan, and Moscow controlled political life.[35] The Ashgabat earthquake of 1948 killed over 110,000 people,[44] amounting to two-thirds of the city's population. A Turkmen man of Central Asia in traditional clothes. Photo by Prokudin-Gorsky between 1905 and 1915. During the next half-century, Turkmenistan played its designated economic role within the Soviet Union and remained outside the course of major world events.[35] Even the major liberalization movement that shook Russia in the late 1980s had little impact.[35] However, in 1990, the Supreme Soviet of Turkmenistan declared sovereignty as a nationalist response to perceived exploitation by Moscow.[35] Although Turkmenistan was ill-prepared for independence and then-communist leader Saparmurat Niyazov preferred to preserve the Soviet Union, in October 1991, the fragmentation of that entity forced him to call a national referendum that approved independence.[35] On 26 December 1991, the Soviet Union ceased to exist. Niyazov continued as Turkmenistan's chief of state, replacing communism with a unique brand of independent nationalism reinforced by a pervasive cult of personality.[35] A 1994 referendum and legislation in 1999 abolished further requirements for the president to stand for re-election (although in 1992 he completely dominated the only presidential election in which he ran, as he was the only candidate and no one else was allowed to run for the office), making him effectively president for life.[35] During his tenure, Niyazov conducted frequent purges of public officials and abolished organizations deemed threatening.[35] Throughout the post-Soviet era, Turkmenistan has taken a neutral position on almost all international issues.[35] Niyazov eschewed membership in regional organizations such as the Shanghai Cooperation Organisation, and in the late 1990s he maintained relations with the Taliban and its chief opponent in Afghanistan, the Northern Alliance.[35] He offered limited support to the military campaign against the Taliban following the 11 September 2001 attacks.[35] In 2002 an alleged assassination attempt against Niyazov led to a new wave of security restrictions, dismissals of government officials, and restrictions placed on the media.[35] Niyazov accused exiled former foreign minister Boris Shikhmuradov of having planned the attack.[35] Between 2002 and 2004, serious tension arose between Turkmenistan and Uzbekistan because of bilateral disputes and Niyazov's implication that Uzbekistan had a role in the 2002 assassination attempt.[35] In 2004, a series of bilateral treaties restored friendly relations.[35] In the parliamentary elections of December 2004 and January 2005, only Niyazov's party was represented, and no international monitors participated.[35] In 2005, Niyazov exercised his dictatorial power by closing all hospitals outside Ashgabat and all rural libraries.[35] The year 2006 saw intensification of the trends of arbitrary policy changes, shuffling of top officials, diminishing economic output outside the oil and gas sector, and isolation from regional and world organizations.[35] China was among a very few nations to whom Turkmenistan made significant overtures.[35] The sudden death of Niyazov at the end of 2006 left a complete vacuum of power, as his cult of personality, comparable to the one of eternal president Kim Il Sung of North Korea, had precluded the naming of a successor.[35] Deputy Prime Minister Gurbanguly Berdimuhamedow, who was named interim head of government, won a non-democratic special presidential election held in early February 2007.[35] His appointment as interim president and subsequent run for president violated the constitution.[45] Berdimuhamedow won two additional non-democratic elections, with approximately 97% of the vote in both 2012[46] and 2017.[47] His son