Muhammad III of Alamut in the context of List of assassinations by the Assassins

The Mongol campaign against the Nizaris of the Alamut period (the Nizari Ismaili state) began in 1253 after the Mongol invasion of the Khwarazmian Empire and a series of Nizari–Mongol conflicts. The campaign was ordered by the Great Khan Möngke and was led by his brother, Hülegü. The campaign against the Nizaris and later the Abbasid Caliphate was intended to establish a new khanate in the region—the Ilkhanate.

Hülegü's campaign began with attacks on strongholds in Quhistan and Qumis amidst intensified internal dissensions among Nizari leaders under Imam Muhammad III of Alamut whose policy was fighting against the Mongols. His successor, Rukn al-Din Khurshah, began a long series of negotiations in face of the implacable Mongol advance. In 1256, the Imam capitulated while besieged in Maymun-Diz and ordered his followers to do likewise according to his agreement with Hülegü. Despite being difficult to capture, Alamut ceased hostilities too and was dismantled. The Nizari state was thus disestablished, although several individual forts, notably Lambsar, Gerdkuh, and those in Syria continued to resist. Möngke Khan later ordered a general massacre of all Nizaris, including Khurshah and his family.

Rukn al-Dīn al-Hasan ibn Muhammad Khurshāh (or Khwarshāh) (ركن الدین الحسن بن محمد خورشاه) (1230–1256) was the son of 'Alā' ad-Dīn Muḥammad III and the 27th Isma'ili Imam. He was also the fifth and final Nizari Isma'ili Imam who ruled at Alamut. The Imam was the eldest son of Imam ʿAla al-Din Muhammad and succeeded his murdered father to the Imamate in 1255. Imam Rukn al-Din engaged in a long series of negotiations with the invading Mongols, and under whose leadership Alamut Castle was surrendered to the Mongol Empire marking the end of the Nizari state in Persia.