Khwarazmshah in the context of "Battle of the Indus"

Between 1219 and 1221, the Mongol forces under Genghis Khan invaded the lands of the Khwarazmian Empire in Central Asia. The campaign, which followed the annexation of the Qara Khitai Khanate, saw widespread devastation and atrocities. The invasion marked the completion of the Mongol conquest of Central Asia, and began the Mongol conquest of Persia.

Both belligerents, although large, had been formed recently: the Khwarazmian dynasty had expanded from their homeland to replace the Seljuk Empire in the late 1100s and early 1200s; nearly simultaneously, Genghis Khan had unified the Mongolic peoples and conquered the Western Xia dynasty. Although relations were initially cordial, Genghis was angered by a series of diplomatic provocations. When a senior Mongol diplomat was executed by Khwarazmshah Muhammed II, the Khan mobilized his forces, estimated to be between 90,000 and 200,000 men, and invaded. The Shah's forces were widely dispersed and probably outnumbered—realizing his disadvantage, he decided to garrison his cities individually to bog the Mongols down. However, through excellent organization and planning, the Mongols were able to isolate and conquer the Transoxianan cities of Bukhara, Samarkand, and Gurganj. Genghis and his youngest son Tolui then laid waste to Khorasan, destroying Herat, Nishapur, and Merv, three of the largest cities in the world. Meanwhile, Muhammed II was forced into flight by the forces of Mongol generals Subutai and Jebe; unable to reach any bastions of support, he died destitute on an island in the Caspian Sea. His son and heir Jalal-al Din managed to mobilize substantial forces, defeating a Mongol general at the Battle of Parwan, but these were crushed by Genghis at the Battle of the Indus a few months later.

The siege of Bukhara took place in February 1220, during the Mongol invasion of the Khwarazmian Empire. Genghis Khan, ruler of the Mongol Empire, had launched a multi-pronged assault on the Khwarazmian Empire ruled by Shah Muhammad II. While the Shah planned to defend his major cities individually, the Mongols laid siege to the border town of Otrar, and struck further into Khwarazmia.

The city of Bukhara was a major centre of trade and culture in the Khwarazmian Empire, but was located far from the border with the Mongol Empire, and so the Shah had allocated fewer than 20,000 soldiers to defend it. A Mongol force, estimated to number between 30,000 and 50,000 men and commanded by Genghis himself, traversed the Kyzylkum Desert, previously considered impassable for large armies. Bukhara's defenders were caught by surprise and, after a failed sortie, the outer city surrendered within three days on 10 February. Khwarazmian loyalists continued to defend the citadel for less than two weeks, before it was breached and taken.

Jalal al-Din Mangburni (Persian: جلال الدین مِنکُبِرنی), also known as Jalal al-Din Khwarazmshah (جلال الدین خوارزمشاه), was the last Khwarazmshah of the Anushtegin dynasty. The eldest son and successor of Ala ad-Din Muhammad II of the Khwarazmian Empire, Jalal al-Din was brought up at Gurganj, the wealthy capital of the Khwarazmid homeland. An able general, he served as second-in-command to his father in at least one battle; however, since he was the son of a concubine, he was challenged as successor by a younger brother, whose cause was supported by the powerful Queen Mother, Terken Khatun. Nevertheless, after the Mongol conquest of the Khwarazmian Empire led to his father's flight and death on an island in the Caspian Sea, Jalal-al Din gained the loyalty of the majority of Khwarazmian loyalists.

The new Shah Jalal al-Din moved to Gurganj, but departed eastwards after Terken Khatun moved against him; evading Mongol patrols, he gathered a substantial army at Ghazni. He managed to inflict an excellent defeat on Shigi Qutuqu at the Battle of Parwan, but soon lost a good portion of his army in a dispute over spoils. He was defeated by a vengeful Genghis Khan at the Battle of the Indus, and fled across the river. Now essentially a warlord, Jalal al-Din managed to establish a succession of short-lived states: first in the Punjab from 1222 to 1224, and then in northwest Iran and Georgia after 1225. Jalal al-Din did not have the political ability needed to underpin his martial exploits, and he was forced to combat several large revolts and increasing pressure from Mongol forces. Eventually, he was killed in 15 August 1231. The army he had gathered would continue to terrorize the Levant as the mercenary Khwarazmiyya until its final defeat in 1246.

Jalal-ud-Din Sultan-Shah, known as Sultan-Shah (died 29 September 1193) was a claimant to the title of Khwarazmshah from 1172 until his death. He was the son of Il-Arslan.

In 1172 Il-Arslan died and his sons began fighting over who would succeed him. Sultan Shah was the younger son, but he was considered the formal heir and his mother, Terken Khatun, placed him on the throne. The elder son, Ala ad-Din Tekish, fled to the Qara Khitai and asked for them to enthrone him in place of his brother, promising an annual tribute in exchange. He was given a large army, and he soon set off for Khwarazm.

The Khwarazmian army, also called the Khwarazmiyya, maintained itself as a force of freebooters and mercenaries between 1231 and 1246, following the Mongol conquest of the Khwarazmian Empire (1221) and the death of the last Khwarazmshah, Jalal al-Din (1231). It was active in Upper Mesopotamia, Anatolia, Syria and Palestine and shifted its allegiance several times, often acting autonomously before it was defeated and destroyed by the Ayyubids.

In 1231, the Khwarazmians were briefly in the service of the Ayyubid governors around Lake Van. Between 1231 and 1237, they were in the service of the Seljukid sultanate of Rum and fought against an Ayyubid invasion in 1232–1233. The Khwarazmians were forced back into Upper Mesopotamia in 1237, during a Seljukid succession crisis. They were then hired by the Ayyubid emir of Damascus. Taking part in the Ayyubid civil wars in Syria, they launched invasions against the emir of Aleppo in 1240 and 1241. Defeated in their second invasion, they retreated to central Mesopotamia and took service with the Abbasid caliphate. Later in 1241, the Khwarazmians hired themselves out to the Zengid emir of Mosul before returning to Syrian Ayyubid politics. They were defeated by Aleppo in 1242.