When Muhammad II of Khwarazm executed a contingent of merchants dispatched by the Mongols, Genghis Khan declared war on the Khwārazm-Shāh dynasty in 1219. The Mongols overran the empire, occupying the major cities and population centers between 1219 and 1221. Iran was ravaged by the Mongol detachment under Jebe and Subutai, who left the area in ruin. Transoxiana also came under Mongol control after the invasion.
Muhammad's son Jalal ad-Din Mingburnu returned to Iran in c. 1224 after fleeing to India. He was overwhelmed and crushed by Chormaqan's army sent by the Great Khan Ögedei in 1231. By 1237 the Mongol Empire had subjugated most of Persia, Azerbaijan, Armenia, most of Georgia, as well as all of Afghanistan and Kashmir. After the battle of Köse Dağ in 1243, the Mongols under Baiju occupied Anatolia, while the Seljuk Sultanate of Rûm and the Empire of Trebizond became vassals of the Mongols.
In 1252, Hulagu was tasked with conquering the Abbasid Caliphate. He was given a fifth of the entire Mongol army for the campaign and he took his sons Abaqa and Yoshmut along with him. In 1258, Hulagu proclaimed himself Ilkhan (subordinate khan).