Mongol Invasion of Central Asia
Driven from China by the Jurchen Jin Dynasty, in 1124 some Khitans moved westward under Yeh-lü Ta-shih’s leadership and created the Kara khitan (Black Khitai, or Western Liao) Khanate between in the Semirechye and the Chu River.
They subdued the Uyghurs, Qarluqs and local Turkic and Tajik peoples.
However, their power was finally 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. The Uyghurs killed an overseer of the Kara-Khitan and declared their allegiance to the Mongols. A Uyghur leader married the daughter of Genghis in order to secure his realm. A leader of the Qarluq and Buzar, the warlord of Chu valley, followed the Uyghur example. Kuchlug usurped the throne and allied with Shah Muhammad of Khorazm.
Fearing of former Christian but now buddhist Kuchlug's persecution, Muslims asked help from the Mongols. Genghis dispatched his general Jebe to conquer the Kara-Khitan. Jebe completed his mission within a few days and Kuchlug died in 1218.
The Mongol invasion of Khwarezmia lasted from 1219 to 1221. It marked the beginning of the Mongol Conquest of the Islamic States, and it also expanded the Mongol invasions, which would ultimately culminate in the conquest of virtually the entire known world, save for Western Europe, Scandinavia, the Byzantine Empire, Arabia, Africa, South Asia, Japan and parts of Southeast Asia.
Ironically, it was not originally the intention of the Mongol Khanate to invade the Khwarezmid Empire. Indeed, Genghis Khan had originally sent the ruler of the Khwarezmid Empire, Ala ad-Din Muhammad , a message greeting him as his equal: "you rule the rising sun and I the setting sun." The Mongols' original unification of all "people in felt tents", unifying the nomadic tribes in Mongolia and then the Turcomens and other nomadic peoples, had come with relatively little bloodshed, and almost no material loss. Even his invasions of China, to that point, had involved no more bloodshed than previous nomadic invasions had caused.
It would be the invasion and utter destruction and complete devastation of the Khwarezmid Empire which would earn - and rightly - the Mongols the name for bloodthirsty ferocity that would mark the remainder of their campaigns. In this brief war, lasting less than two years, not only was a huge empire destroyed utterly, but Genghis Khan introduced the world to tactics that would not be seen again until the Germans used them so well in World War II - indirect attack, and complete and utter terror and slaughter of populations wholesale as weapons of war.