Mongol campaigns in Central Asia

Mongol campaigns in Central Asia occurred after the unification of the Mongol and Turkic tribes on the Mongolian plateau in 1206. Smaller military operations of the Mongol Empire in Central Asia included the destruction of surviving Merkit and Naimans (which involved forays into Cumania) and the conquest of Qara Khitai. These were followed by a major campaign against Khwarazm. Expansion into Central Asia began in 1209 as Genghis Khan sent an expedition to pursue rivals who had fled to the region and threatened his new empire. The Uyghur kingdom Qocho and leaders of the Karluks submitted voluntarily to the Mongol Empire and married into the imperial family. By 1218 the Mongols controlled all of Xinjiang and by 1221 all the territories of the former Khwarazmian Empire. In 1236, the Mongols defeated the eastern portions of Cumania and swept into Eastern Europe.
The Merkit had a long-standing feud with the Borjigin clan to which Temujin, the future Genghis Khan, belonged. They and the Naimans opposed the rise of Genghis Khan. They joined with the forces of Jamukha and Toghrul to oppose Temujin in the Battle of Chakirmaut in 1204. Temujin defeated the alliance, and the surviving Merkit and Naimans fled into Western Siberia, where they eventually gathered at the Irtysh. Temujin's victory against the alliance consolidated his control of the Mongol and Turkic tribes in the region. In 1206, he was elected the khan of the new Mongol Empire and given the name Genghis Khan. In either late 1208 or early 1209, as part of the conquest of Siberia, a Mongol expedition commanded by Genghis Khan's oldest son, Jochi, met the Merkits and Naimans at a branch of the Irtysh. The Merkit commander Toqto'a was killed in action, and many of his soldiers drowned in the river attempting to flee.
The Merkits and Naimans who survived the battle regrouped at the Chu but were again defeated. The surviving Merkit fled first to the Uyghurs approaching Turpan. After the Uyghurs allied with the Mongols, they fled west, past Qara Khitai to the Qangli Kipchaks of Cumania. The Naiman leader Kuchlug fled south to Qara Khitai. The Merkit might have accompanied him briefly, but soon made their way further west.
The initial contact with, and legacy of, the Mongol Empire with Central Asia was peaceful and not destructive, as the empire's nearest neighbors in Eastern Turkestan tenured their submission to the Mongols voluntarily. After their defeat at the Battle of the Irtysh, the surviving Merkit, led by Qudu, fled to the territory of the Uyghur kingdom of Qocho. However, the ruler, Barchuq Art Tegin, was chafing at the increasing demands from Qara Khitai and killed both the Merkit envoys sent to him as well as the viceroy of the Qara Khitai. In 1209, Barchuq voluntarily joined the Mongol Empire, making the Uyghurs one of the first Turkic groups to do so. To solidify the alliance, Al Altun, the youngest daughter of Genghis Khan and his chief consort Börte, was married to Barchuq. Their submission was perhaps unexpected, as the presence of the Mongol armies in the region might have had such submission as a goal in addition to pursuing Genghis's rivals. The Uyghur contributed administrative and linguistic expertise to Mongols, in exchange for their military protection. Because they submitted voluntarily, they were granted vassal status. Barchuq was allowed to operate independently, and his kingdom contributed 18,000 troops to the Western campaigns, including the conquest of Qara Khitai, Khwarazm, and Western Xia, and possibly participating in the Battle of the Chem against surviving Merkit.
In 1211, the Karluks, a Turkic confederation the area of the southern Ili, in the Tarbagatai Mountains and northern Xinjiang, also voluntarily submitted to the Mongols. The ruler Arslan Khan married a junior daughter of Genghis Khan, who possibly went by the name Töre or Tolai. Arslan commanded six thousand men. Another Karluk leader, Ozar of Almaliq, married a daughter of Jochi. He commanded an unknown number of soldiers. Because the Karluks submitted voluntarily like the Uyghur, their military was allowed to operate as an auxiliary without integrating into the main, atomized army. By 1218, the Mongol Empire controlled all of what is present-day Xinjiang.
At some point likely between 1209 and 1219, most likely 1217 or 1218, General Subutai was dispatched to deal with the Merkit survivors and he, Jebe, and Tuqachar, likely joined in force with a Uyghur army, met the Merkit at the Chem River, in what is present-day western Kazakhstan, and destroyed them. The Merkit and Qangli Kipchak allies who survived fled to what is now northern Kazakhstan. Jebe and Subutai pursued and defeated them. At this juncture, Jebe and Subutai did not attempt to incorporate the Qangli into the empire. Having completed their destruction of the Merkit, they returned home. The independent nomadic tribes that the Mongols had encountered in Central Asia and Eastern Europe may have been at least part of the impetus for Ögedei Khan to launch a western campaign in 1235. In 1236, the westward expansion of Batu Khan, the son of Jochi, smashed into the Kipchaks, beginning an invasion of Europe, and incorporated the Kipchak lands in Central Asia, Eastern Europe, and Western Siberia into his appanage, which became known as the Golden Horde.
The Qara Khitai (Black Khitan) were Khitans of the Liao Dynasty (907–1125) who were driven out of China by the Jurchens of the Jin dynasty. In 1124 some Khitans moved westward under Yeh-lü Ta-shih’s leadership and created the Qara Khitai Khanate (Western Liao) between in the Semirechye and the Chu River. They dominated Central Asia in the 12th century after they defeated the Great Seljuk leader Ahmed Sanjar at the Battle of Qatwan in 1141. However, their power was shattered in 1211 through the combined actions of the Khwārezm-Shah ʿAlāʾ ad-Dīn Muḥammad (1200–20), and Küchlüg, a fugitive Naiman prince in flight from Genghis Khan’s Mongols. Kuchlug was given shelter by the Qara Khiitai, but he usurped the Gurkhan's throne in 1211.
Kuchlug attacked the Karluk city of Almaliq, and the Karluks appealed to Genghis Khan for help. In 1216, Genghis dispatched his general Jebe to pursue Kuchlug. The Mongols defeated the Qara Khitai at Balasaghun, Kuchlug fled, but was killed in 1218 after his capture in Badakhshan in Afghanistan.
According to Juvaini, Genghis Khan had originally sent the ruler of the Khwarezmid Empire, Sultan Muhammad Aladdin, a message seeking trade and greeted him as his neighbor: "I am master of the lands of the rising sun while you rule those of the setting sun. Let us conclude a firm treaty of friendship and peace." or he said, "I am Khan of the lands of the rising sun while you are sultan those of the setting sun: Let us conclude a firm agreement of friendship and peace."
However, the Governor of Otrar refused to receive the mission and had all 450 of them killed, with permission from the Sultan. Upon hearing of this atrocity months later, Genghis Khan flew into a rage and used the incident as a pretext for invasion. The Mongol invasion of Central Asia however would entail the utter destruction of the Khwarezmid Empire along with the massacre of much of the civilian population of the region. According to Juvaini, the Mongols ordered only one round of slaughter in Khwarezm and Transoxiana, but systematically exterminated a particularly large portion of the people of the cities of Khorasan. This earned the Mongols a reputation for bloodthirsty ferocity that would mark the remainder of their campaigns.