After the death of Muhammad, he was succeeded by 'the Rashidun', a 30-year reign of the four 'rightly guided caliphs'. During such reign, which lasted from 632 CE to 656 CE, the expansion through the territories outside Arabia started.
Eventually, under the influence of the political systems of these territories, the leadership became hereditary, and the Umayyad dinasty, who moved to Damascus to excercise power, ruled from 661 CE to 750 CE. This dinasty achieved the greatest expansion of the Muslim Empire in a lapse of 89 years, converting the Caucasus, Transoxiana, Sindh, the Maghreb, and the Iberian Peninsula to Islam, as well as occupying 5.79 million square miles of territory and including 62 million people. It was the fifth largest empire in history regarding area and proportion of the world's population.