Khwarazmian army between 1231 and 1246

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.

The Khwarazmians made an alliance with the Ayyubid sultan of Egypt in 1243. In 1244, they invaded Palestine, sacked Jerusalem and defeated the anti-Egyptian alliance at the Battle of Forbie. Thus they permanently ended Crusader rule in Jerusalem. In 1245, they helped the Egyptians conquer Damascus. Dissatisfied with their rewards, they rebelled in 1246 and besieged Damascus. They suffered a crushing defeat at the hands of an alliance led by Aleppo, and disintegrated as a unified force.