Many social changes took place under Islam between 610 and 661, including the period of Muhammad's mission and the rule of his four immediate successors who established the Rashidun Caliphate. According to William Montgomery Watt, for Muhammad, religion was not a private and individual matter but rather "the total response of his personality to the total situation in which he found himself. He was responding [not only]... to the religious and intellectual aspects of the situation but also the economic, social, and political pressures to which contemporary Mecca was subject."