The dynasty was founded by commander Anush Tigin Gharchai, a former Turkish slave of the Seljuq sultans, who was appointed as governor of Khwarezm. His son, Qutb ad-Din Muhammad I, became the first hereditary Shah of Khwarezm.
in The Levant
The date of the founding of the Khwarazmian dynasty remains debatable. During a revolt in 1017, Khwarezmian rebels murdered Abu'l-Abbas Ma'mun and his wife, Hurra-ji, sister of the Ghaznavid sultan Mahmud. In response, Mahmud invaded and occupied the region of Khwarezm, which included Nasa and the ribat of Farawa. As a result, Khwarezm became a province of the Ghaznavid Empire from 1017 to 1034. In 1077 the governorship of the province, which since 1042/1043 belonged to the Seljuqs, fell into the hands of Anush Tigin Gharchai, a former Turkic slave of the Seljuq sultan. In 1141, the Seljuq Sultan Ahmed Sanjar was defeated by the Qara Khitai at the battle of Qatwan, and Anush Tigin's grandson Ala ad-Din Atsiz became a vassal to Yelü Dashi of the Qara Khitan.
Sultan Ahmed Sanjar died in 1156. As the Seljuk state fell into chaos, the Khwarezm-Shahs expanded their territories southward. In 1194, the last Sultan of the Great Seljuq Empire, Toghrul III, was defeated and killed by the Khwarezm ruler Ala ad-Din Tekish, who conquered parts of Khorasan and western Iran. In 1200, Tekish died and was succeeded by his son, Ala ad-Din Muhammad, who initiated a conflict with the Ghurids and was defeated by them at Amu Darya (1204). Following the sack of Khwarizm, Muhammad appealed for aid from his suzerain, the Qara Khitai who sent him an army. With this reinforcement, Muhammad won a victory over the Ghorids at Hezarasp (1204) and forced them out of Khwarizm.
Ala ad-Din Muhammad's alliance with his suzerain was short-lived. He again initiated a conflict, this time with the aid of the Kara-Khanids, and defeated a Qara-Khitai army at Talas (1210), but allowed Samarkand (1210) to be occupied by the Qara-Khitai. He overthrew the Karakhanids (1212) and Ghurids (1215). In 1212, he shifted his capital from Gurganj to Samarkand. Thus incorporating nearly the whole of Transoxania and present-day Afghanistan into his empire, which after further conquests in western Persia (by 1217) stretched from the Syr Darya to the Zagros Mountains, and from the northern parts of the Hindu Kush to the Caspian Sea. By 1218, the empire had a population of 5 million people.