During the reign of the Abassid Dynasty (758-1258) in the Islamic Empire , in 813, a man called Abd Allah seized power from his brother, the Caliph who was called al-Amin. Abd Allah became known as al-Ma'mun and was one of the most competent , radical, and important rulers of the Abassid Dynasty.
One of the big problems at the time was the incorporation of Shi'ite Muslims into the empire, but this was, as it had been before him, very controversial among Shi'ites' and anti-Shi'ites alike. al-Ma'mun had to spend most of his time quelling disturbances, barely holding together the Abassid Empire (The Caliphate at this time had grown very weak).
Because of this constant state of unrest, he decided that he needed an army that was loyal only to the Caliph. His brother, al-Mu'tasim, who would later become caliph assembled a force of military slaves and called them Mamluks. The Mamluk army consisted of Turks, famous for their horsemanship, and also a good bit of Slavs and Berbers. The Mamluks became so powerful that they eventually displaced the Arab and Persian armies as the major military force in the Islamic World. This of course, pissed off many people in Arabia and Persia, and soon the people of the empire began to grow weary of the Caliphate, which they felt was overexerting its power. The Mamluks also represented a new ethnic group to come to power in the Islamic World and play an importnat role in the decline of medieval Islam (and the eventual rise of a Turkish Dynasty, the Seljuks and then the Ottomans)
Another important innovation of al-Ma'mun's was his patronization of Greek, Sanskrit, and Arabic learning so that his empire became a scientific and intellectual powerhouse. He took a radical theological position, Mu'tazilism, regarded as heretical by more orthodox Muslims. The basic principle was that all Muslims should obey a single ruler, and he sure as hell didn't mean Allah. To spread his religious and philosophical teaching he established the university bayt al-Hikma, 'The House of Wisdom'.
It was at this time that the great works of the Hellenistic World and the India were incorporated into Islamic culture through a series of translations. The Hellenistic method of inquiry became part of Islamic tradition, and for this reason, the works of Plato and Aristotle were passed on to future generations, and eventually back into the West. The new Islamic intellectual practice, called faylaaSafa 'philosophy' was based on the principles of rational inquiry as well as some empiricism.