The majority of the Shi'ites, from whom the previously mentioned groups have branched out, are Twelve-Imam Shi'ites, also called the Imamites. As has already been mentioned, the Shi'ites came into being because of criticism and protest concerning two basic problems of Islam, without having any objections to the religious ways which through the instructions of the Prophet had become prevalent among their contemporary Muslims. These two problems concerned Islamic government and authority in the religious sciences, both of which the Shi'ites considered to be the particular right of the Household of the Prophet.
The Shi'ites asserted that the Islamic caliphate, of which esoteric guidance and spiritual leadership are inseparable elements, belongs to Ali and his descendants. They also believed that according to the specification of the Prophet the Imams of the Household of the Prophet are twelve in number. Shi'ism held, moreover, that the external teachings of the Quran, which are the injunctions and regulations of the Shari'ah and include the principles of a complete spiritual life, are valid and applicable for everyone at all times, and are not to be abrogated until the Day of Judgment. These injunctions and regulations must be learned through the guidance of the Household of the Prophet.
From a consideration of these points it becomes clear that the difference between Twelve-Imam Shi'ism and Zaydism is that the Zaydis usually do not consider the imamate to belong solely to the Household of the Prophet and do not limit the number of Imams to twelve. Also they do not follow the jurisprudence of the Household of the Prophet as do the Twelve-Imam Shi'ites. The difference between the Twelve-Imam Shi'ism and Isma'ilism lies in that for the latter the imamate revolves around the number seven and prophecy does not terminate with the Holy Prophet Muhammad. Also for them, change and transformation in the injunctions of the Shari'ah are admissible, as is even rejection of the duty of following Shari'ah, especially among the Batinis.
In contrast, the Twelve-Imam Shi'ites consider the Prophet to be the "seal of prophecy" and believe him to have twelve successors and executors of his will. They hold the external aspect of the Shari'ah to be valid and impossible to abrogate. They affirm that the Quran has both an exoteric and an esoteric aspect. Summary of the History of Twelve-Imam Shi'ism As has become clear form the previous pages, the majority of Shi'ites are Twelvers. They were originally the same group of friends and supporters of Ali who, after the death of the Prophet, in order to defend the right of the Household of the Prophet in the question of the caliphate and religious authority, began to criticize and protest against prevalent views and separated from the majority of the people. During the caliphate of the "rightly-guided caliphs" (11/632-35/656) the Shi'ites were under a certain amount of pressure which became much greater during the Umayyad Caliphate (40/661-132/750) when they were no longer protected in any way against destruction of their lives and property.
Yet the greater the pressure placed upon them, the firmer they became in their belief. They especially benefited from their being oppressed in spreading their beliefs and teachings. From the middle of the 2nd/8th century when the Abbasid caliphs established their dynasty, Shi'ism was able to gain a mew life as a result of the languid and weak state prevailing at that time. Soon, however, conditions became difficult once again and until the end of the 3rd/9th century became ever more stringent.
At the beginning of the 4th/10th century, with the rise of the influential Buyids, who were Shi'ites, Shi'ism gained power and became more or less free to carry out its activities. It began to carry out scientific and scholarly debates and continued in this manner until the end of the 5th/11th century. At the beginning of the 7th/13th century when the Mongol invasion began, as a result of the general involvement in war and chaos and the continuation of the Crusades, the different Islamic governments did not put too great a pressure upon the Shi'ites. Moreover, the conversion to Shi'ism of some Mongol rulers in Persia and the rule of the Sadat-i Mar'ashi (who were Shi'ites) in Mazandaran were instrumental in the spread of the power and territory of Shi'ism. They made the presence of large concentrations of Shi'ite population in Persia and other Muslim lands felt more than ever before.
This situation continued through the 9th/15th century. At the beginning of the 10th/16th century, as a result of the rise of the Safavids, Shi'ism became the official religion of the vast territories of Persia and continues in this position to the present day. In other regions of the world also there are tens of millions of Shi'ites.