In 909, Abdullah al-Mahdi Billah, a claimant to the Ismaili Imamate, established the Fatimid Caliphate. The Sultanate of Aussa (Afar Sultanate) succeeded the earlier Imamate of Aussa. The Sultanate of Aussa or "Afar Sultanate" succeeded the earlier Imamate of Aussa. Under Azzan, the country briefly reverted to being an imamate, rather than a sultanate. Al-Askari's death coincided with the beginning of the imamate of the Mahdi. Al-Sadiq's death led to uncertainty about the succession of the Imamate. In several supplications Imam Sajjad explains the concept of Imamate (leadership). The global seat of the Ismaili Imamate is in Lisbon, Portugal. He was the founder of the Zaidi imamate in 897. The Shia belief throughout its history split over the issue of the Imamate. The first Imamate reached its peak power in the ninth A.D. century. After the Crimean War, Russia redoubled its efforts against the Imamate. Besides, the basis of Shia school is in terms of imamate or leadership. The Treaty of Seeb was terminated and the autonomous Imamate of Oman abolished. Shamil agreed, and The Caucasian Imamate was no more.