Shi‘a Islam, also known as Shi‘ite Islam or Shia, is the second largest branch of Islam after Sunni Islam. Shias adhere to the teachings of Muhammad and the religious guidance of his family (who are referred to as the Ahl al-Bayt) or his descendants known as Shia Imams. Muhammad's bloodline continues only through his daughter Fatima Zahra and cousin Ali who alongside Muhammad's grandsons comprise the Ahl al-Bayt. Thus, Shias consider Muhammad's descendants as the true source of guidance along with the teaching of Muhammad. Shia Islam, like Sunni Islam, has at times been divided into many branches; however, only three of these currently have a significant number of followers, and each of them has a separate trajectory.
From a political viewpoint the history of the Shia was in several stages. The first part was the emergence of the Shia, which starts after Muhammad's death in 632 and lasts until Battle of Karbala in 680. This part coincides with the Imamah of Ali, Hasan ibn Ali and Hussain. The second part is the differentiation and distinction of the Shia as a separate sect within the Muslim community, and the opposition of the Sunni caliphs. This part starts after the Battle of Karbala and lasts until the formation of the Shia states about 900. During this section Shi'ism divided into several branches. The third section is the period of Shia states. The first Shia state was the Idrisid dynasty (780–974) in Maghreb. Next was the Alavid dynasty (864–928) established in Mazandaran (Tabaristan), north of Iran. These dynasties were local, but they were followed by two great and powerful dynasties. The Fatimid Dynasty formed in Ifriqiya in 909, and ruled over varying areas of the Maghreb, Egypt and the Levant until 1171. The Buyid dynasty emerged in Daylaman, in the north of present-day Iran, in about 930 CE and then ruled over central and western parts of Iran and Iraq until 1048. As a result, the period from the mid-10th to the mid-11th century is often known as the "Shi'a Century" of Islam. In Yemen, Imams of various dynasties usually of the Zaidi sect established a theocratic political structure that survived from 897 until 1962. Iran, formerly of Sunni majority region underwent a process of forced conversion to Shia Islam under the Saffavids between the 16th and 18th century. The process also ensured the dominance of the Twelver sect within Shiism over the Zaidiyyah and sects of Isma'ilism in the modern day.
