M. I. Naved & M. H. Syed 
Encyclopaedia of Islamic Empires and Dynasties (First Islamic Head of State) [PDF ebook] 

As is well known and appreciated by all scholarly circles, Islam is ideologically against the imperialism and hierarchy. With the demise of Holy Prophet, his close companions decided to select a leader to lead the Muslims. This leader was known as the khalifa or caliph. First, there were four caliphs, called, Pious Caliphs or Righteous Caliphs. Then, the first Islamic dynasty was established by Umayyad family, who established the practice of hereditary succession. Umayyads were overthrown by Abbasids. The most important event in this era was the series of Crusades between Muslims and Christians. Ghazi Salahuddin, the great Muslim hero, finally defeated the Crusaders. When Abbasids captured Damascus, one of the Umayyad princes had escaped to Spain to found Umayyad rule there. The Muslims ruled over Spain for nearly eight centuries. In Persia, a new dynasty called Safavids came to power. Then, emerged Zand dynasty, which was overthrown by Qajars and they were in turn replaced by Pahlavis. In east, Mongols converted to Islam and became known as the Il-Khanids. They were succeeded by Timur and his descendents. Later, Ottomans or Turks became the dominant power in the Islamic world. They conquered much of eastern Europe and nearly the whole of the Arab world. This research-based work is a thorough study of the rise of Islam and its journey to success over a millennia. This is an asset for all scholars and lovers of Islamic Studies.