By AD 640, Syria was conquered by the Arab Rashidun army led by Khalid ibn al-Walid. In the mid-7th century, the Umayyad dynasty, then rulers of the empire, placed the capital of the empire in Damascus. The country's power declined during later Umayyad rule; this was mainly due to totalitarianism, corruption and the resulting revolutions. The Umayyad dynasty was then overthrown in 750 by the Abbasid dynasty, which moved the capital of empire to Baghdad.