Islam / Caliph /
The Abbasids governed from Baghdad, a city the second Abbasid Caliph founded in 762, and Samara for some periods in the 9th century. The Abbasids took the power from the Umayyads in 750, and stayed in power until the Mongols conquered Baghdad in 1258, and had the Caliph killed.
For their first 100 years, the Abbasids were leaders, both of Islam and of the Muslim community. The Shi'is of the period rejected the legitimacy of the Abbasid leadership.
The change came towards the end of the 9th century, and started with the takeover by Sunni scholars of religious leadership, of the cost of the Caliph. This change became especially clear after the Mihna of mid-9th century.
In political terms, the Abbasid Caliphs became puppets in the hands of the Turkish military troops, and in 935 the title Emiru l-Umara was transferred to the chief of the Turkish soldiers.
The Persian Shi'i Buwayhids were the real rulers from 945 until the 10th century. The Buwayhids were so strong that they had the power to remove Caliphs at their own will.
At the same time as the Caliphs lost the grip of power, the unity of the Caliphate also fell apart, and independent states were formed. These new states recognized the position of the Caliph, but it was only the symbolic value that survived.
In 1055 the Turkish Seljuqs conquered Baghdad, but this had little influence to the position of the Caliphs, who continued to play only his limited symbolical role. With the fall of the traditional Caliphate in 1258, when the Mongols took over Baghdad, a new line of Abbasid Caliphs continued in Cairo. In Cairo they played the same type of role as in Baghdad, but now even the symbolical role was limited by geography. This, the last branch of Abbasids, stayed in office until 1517.
Harunu r-Rashid is the most famous of the Abbasid Caliphs. The Abbasid period, is recognized of being the one in Muslim history bringing the most elevated scientific works. The Muslim world continued the achievements of classical Europe (especially the 9th and 10th centuries), India and former science of the Middle East, during a period when Europe was unable contribute much to the cultural and scientific fields. The Abbasid era is often regarded as the golden age of Muslim civilization.