Hulagu's brother Möngke Khan had been installed as Great Khan in 1251.
Möngke charged Hulagu with leading a massive Mongol army to conquer or destroy the remaining Muslim states in southwestern Asia.
Hulagu's campaign sought the subjugation of the Lurs of southern Iran, the destruction of the Nizari Ismaili state (the Assassins), the submission or destruction of the Abbasid Caliphate in Baghdad, the submission or destruction of the Ayyubid states in Syria based in Damascus, and finally, the submission or destruction of the Bahri Mamluke Sultanate of Egypt.
Möngke ordered Hulagu to treat kindly those who submitted and utterly destroy those who did not.
Hulagu vigorously carried out the latter part of these instructions.

Hulagu marched out with perhaps the largest Mongol army ever assembled – by order of Möngke, two-tenths of the empire's fighting men were gathered for Hulagu's army in 1253.
He arrived at Transoxiana in 1255.
He easily destroyed the Lurs, and the Assassins surrendered their impregnable fortress of Alamut without a fight, accepting a deal that spared the lives of their people in early 1256.
Although the castle was surrendered during the Mongol invasion of Alamut, the Ismailis were captured and massacred without a second thought.
This devastation led to the assumption that the community and most of its literature had perished.

Hulagu Khan chose Azerbaijan as his power base, while ordering Baiju to retreat to Anatolia.
Hulagu's brother Möngke Khan had been installed as Great Khan in 1251. Möngke charged Hulagu with leading a massive Mongol army to conquer or destroy the remaining Muslim states in southwestern Asia. Hulagu's campaign sought the subjugation of the Lurs of southern Iran, the destruction of the Nizari Ismaili state (the Assassins), the submission or destruction of the Abbasid Caliphate in Baghdad, the submission or destruction of the Ayyubid states in Syria based in Damascus, and finally, the submission or destruction of the Bahri Mamluke Sultanate of Egypt. Möngke ordered Hulagu to treat kindly those who submitted and utterly destroy those who did not. Hulagu vigorously carried out the latter part of these instructions.
Hulagu marched out with perhaps the largest Mongol army ever assembled – by order of Möngke, two-tenths of the empire's fighting men were gathered for Hulagu's army in 1253. He arrived at Transoxiana in 1255. He easily destroyed the Lurs, and the Assassins surrendered their impregnable fortress of Alamut without a fight, accepting a deal that spared the lives of their people in early 1256. Although the castle was surrendered during the Mongol invasion of Alamut, the Ismailis were captured and massacred without a second thought. This devastation led to the assumption that the community and most of its literature had perished.
Hulagu Khan chose Azerbaijan as his power base, while ordering Baiju to retreat to Anatolia.
Hulagu Khan