Caliphate
Caliphate (“Khilafat” in Arabic) was a semi-religious political system of governance in Islam, in which the territories were ruled by a supreme leader called Caliph (“Khalifa” in Arabic – meaning successor). Caliphs were initially selected by a group of senior members of the followers of Muhammad. The first four caliphs, who were nominated in such a way, are referred to as the Rashidun (rightly guided) caliphs by mainstream Sunni Muslims; Shia Muslims consider only Ali, the fourth one, to be legitimate and discard the claims of the first three by branding them as usurpers.
Below is a picture of the Dome of the New Mosque, in the Hagia Sophia, Istanbul. It shows the four medals of the names of the first four Rashidun Caliphs: Abu Bakr (632 - 634 CE), Umar (634 - 644 CE), Uthman (644 - 656 CE) and Ali (656 - 661 CE).
The caliphate soon became a hereditary institute when the dynastic system of rule was introduced to the Islamic world by the Umayyads, who were overthrown and replaced by the Abbasids. The Abbasids, after the destruction of Baghdad in 1258 CE, held nothing but the title itself. This was to change when the Ottoman Sultans took over the institute, becoming the first and last non-Arabs to do so, and continued it until 1924 CE when it was officially abolished by Turkish nationalist leader Mustafa Kemal Pasha (the father of modern Turkey).
Here is a list of caliphates:
Rashidun Caliphate (632–661)
Umayyad Caliphate (661–750)
Abbasid Caliphate (750–1517)
Ottoman Caliphate (1517–1924).
A book describing the caliphs up to 710 CE is provided below. It is the second volume of a two-volume book, the first volume covering the life of Prophet Muhammad.
Below is information about the author from Wikipedia:
"Washington Irving (April 3, 1783 – November 28, 1859) was an American short-story writer, essayist, biographer, historian, and diplomat of the early 19th century. He is best known for his short stories "Rip Van Winkle" (1819) and "The Legend of Sleepy Hollow" (1820), both of which appear in his collection The Sketch Book of Geoffrey Crayon, Gent. His historical works include biographies of Oliver Goldsmith, Muhammad and George Washington, as well as several histories of 15th-century Spain that deal with subjects such as Alhambra, Christopher Columbus and the Moors. Irving served as American ambassador to Spain in the 1840s."