Dynasty that ruled the Islamic caliphate from the death of the fourth Sunni caliph Hazrat Ali, in 661 until 750. Its founder was Ameer-Muawiyah ibn Abi Sufyan of the Meccan clan of Umayyah. By the time of Muawiyah's death in 680, he had established Damascus as the capital and a system of administration for the caliphate that gave it a degree of stability. A later caliph, Abd al-Malik, strengthened the organization of the empire, making Arabic the official language of government and replacing Byzantine and Sassanian coinage with coins with Arabic inscriptions. At times tribal rivalries threatened the unity of the empire. The dynasty was responsible for the expansion of the Islamic state westward through North Africa to the Atlantic Ocean. In 711 the Umayyads crossed into the Iberian peninsula and rapidly conquered most of it, establishing a forward base in southern France. They were defeated between Tours and Poitiers in 732 by Charles Martel, halting the expansion of Islam into western Europe. In the East, they moved from Iran into Central Asia and northwest India. Little progress was made in the North due to the strength of the Byzantine Empire. The Umayyads’ great expansion was primarily military and political, not religious; conversion to Islam was discouraged for some time since it would reduce the treasury's intake of taxes on non-Muslims. Its armies were originally exclusively Arab and Muslim, but clients were ultimately included, mostly of Iranian and Berber origin. Later Muslim historians accused the Umayyads of transforming the Islamic state into an Arab kingdom. The Umayyads did rely largely on the traditional political ideas of Arabs, but they also claimed to be upholders of Islam. Overthrown by Abbasids in 750.