Each caliphate had its own instabilities. First, the Four Orthodox Caliphs dealt with several issues such as blood feuds, no continuation of government after each caliph, and lack of government for the amount of land. Tribal feuds and civil wars plagued these caliphs beginning with the War of Fitnah. Because these four caliphs did not follow ancestral succession, each new caliph set up his own government, often in a different capitol city. Under these caliphs, generals were sent out to conquer the world. While much land was taken in Persia, Syria, Jordan, Turkey, and Northern Africa, the Muslim government was not strong enough to govern so much territory.
Second, under the Umayyads the caliphate faced different problems. Government did continue under the ancestral line, but it still struggled to control the vast amounts of land. Because these caliphs enjoyed riches and lived luxuriously, they were despised and many were murdered. The Muslims during this time wished to return to the simpler Bedouin lifestyle. The Abbasids slew all but one Umayyad, Al-Rahmin, who took his people to Spain and established a kingdom there.
During the Abbasid reign, the caliphs promised peace and reform. Outside forces such as Turkish mercenaries aided the downfall of the Abbasids because of the power the Turks gained as vizirs. Several other Muslim groups broke off from the Abbasids such as the Idrisids in Morocco and the Aghlabids in Tunisia. Because all of the factors were added together, the caliphate lost complete control in 861 and opened the door for others to come in.
– Hannah S. Bowers