sentences:  This marked the permanent and enduring split of the Isma'ili movement into the rival "Musta'li" and "Nizari" branches.Hassan-i Sabbah founded the Nizari Order of Assassins, which was responsible for the assassination of al-Afdal in 1121, and of al-Musta'li's son and successor al-Amir bi-Ahkam Allah (who was also al-Afdal's nephew and son-in-law) in October 1130.This led to a succession of coups and crises that heralded the final decline, and eventual collapse, of the Fatimid state.