The Mongol invasion of Persia, which began in 1220, together with the subsequent fall of the Baghdad caliphate and the killing of the last ‘Abbāsid caliph, al-Musta‘sim billāh, brought the entire Muslim world and especially Persia face to face with unexpected and formidable problems. The Mongol invasion, then, strengthened the non-Muslim communities in Persia. At the time of the Mongol invasion two tariqas had a predominant influence in Iran: the Kubrāviyya in the East and the Suhravardiyya in the West. In the history of religion in Iran, the Mongol period is important for a number of reasons. First, it saw a strengthening of Shī‘sm as a consequence of the fall of the ‘Abbāsid caliphate, and this was accompanied by a proportionate mitigation of the Shī‘ī-Sunnī dispute, the appearance within Shī‘sm of trends towards Shī‘sm, and a leaning towards a certain tashayyu' hasan ("moderate" Shī‘sm) in Sunni circles. And finally, Shī‘sm made particularly noteworthy progress, especially in its doctrinal tendencies.