throne, the Sasanian Empire was plunged into several years of dynastic turmoil and civil war. The Sasanians were further weakened by economic decline, heavy taxation from Khosrau II's campaigns, religious unrest, and the increasing power of the provincial landholders. The Byzantine Empire was also severely affected, with its financial reserves exhausted by the war and the Balkans now largely in the hands of the Slavs. Additionally, Anatolia was devastated by repeated Persian invasions; the Empire's hold on its recently regained territories in the Caucasus, Syria, Mesopotamia, Palestine and Egypt was loosened by many years of Persian occupation. Neither empire was given any chance to recover, and according to George Liska, the "unnecessarily prolonged Byzantine–Persian conflict opened the way for Islam". The Quraysh ruled the city of Mecca, and expelled their member Muhammad from it to the city of Medina in 622, from where he began spreading his new religion, Islam. In 631 Muhammad marched with 10,000 to Mecca and conquered it before dying the next year. His successors united most of Arabia in the Ridda wars (632-633) and then started the Muslim conquests of the Levant (634-641), Egypt (639-642) and Persia (633-651), the latter ending the Sasanian empire. In less than a decade after his death, the Islamic Rashidun Caliphate extended its reach from Atlas Mountains in the west to the Hindu Kush in the east. However, the First Fitna led to its replacement by the Umayyad Caliphate in 661, moving the centre of power to Damascus. At its height, the Umayaads ruled a third of the world's population. In 750, the Abbasid Caliphate replaced the Umayyads in the Abbasid Revolution. In 762, they moved the capital to Baghdad. The Emirate of Córdoba remained under Umayaad rule, while in 788 the Idrisid dynasty broke away in Morocco. The Fatimid Caliphate started taking over North Africa from 909 onwards, and the Buyid dynasty broke away in Persia and later Mesopotamia starting in the 930's.In 711, the Umayyad conquest of Hispania began, and in 717 they crossed the Pyrenees into the European Plain. They were met by the Merovingian dynasty, which had been established by Clovis I (481-511), which was in decline, leading Charles Martel to seize power and defeat the invasion force at the Battle of Tours in 732. His son Pepin the Short established the Carolingian dynasty in 751. Charlemagne (768-814) turned it into the Carolingian Empire, being crowned Emperor