A caliphate or khilāfah is an institution or public office under the leadership of an Islamic steward with the title of caliph, a person considered a political-religious successor to the Islamic prophet Muhammad and a leader of the entire Muslim world (ummah). Historically, the caliphates were polities based on Islam which developed into multi-ethnic trans-national empires. During the medieval period, three major caliphates succeeded each other: the Rashidun Caliphate (632–661), the Umayyad Caliphate (661–750), and the Abbasid Caliphate (750–1517). In the fourth major caliphate, the Ottoman Caliphate, the rulers of the Ottoman Empire claimed caliphal authority from 1517 until the caliphate was formally abolished as part of the 1924 secularisation of Turkey. Throughout the history of Islam, a few other Muslim states, almost all of which were hereditary monarchies such as the Mamluk Sultanate (Cairo) and Ayyubid Caliphate, have claimed to be caliphates.