Growing dissatisfaction with the caliphs increasingly luxurious lifestyle helped spark revolts against the government.
The massive spread of the empire also led to its downfall as many began settling in the borderlands, thus identifying themselves with that area rather than their leaders in far away Damascus.
Settled warriors also saw their portions of funds dwindle despite having earned it by fighting in wars of expansion – discontented, they joined forces under the Abbasid party and began openly attacking the Umayyad.
Those who had converted to Islam, but never enjoyed the full benefits soon threw their support behind the Abbasids, as did the Shi-ites, who had opposed the Umayyads from the beginning. After defeating the Umayyads in battle, the Abbasids offered a reconciliation dinner – all a farce to get the Umayyad family in one place so they could be slaughtered.
The Umayads were the first Muslim dynasty — that is, they were the first rulers of the Islamic Empire to pass down power within their family.
According to tradition, the Umayyad family (also known as the Banu Abd-Shams) and Muhammad (peace and blessings of Allāh be upon him) both descended from a common ancestor, Abd Manaf ibn Qusai, and they originally came from the city of Mecca.
Muhammad (peace and blessings of Allāh be upon him) descended from Abd Manāf via his son Hashim, while the Umayyads descended from Abd Manaf via a different son, Abd-Shams, whose son was Umayya. The two families are therefore considered to be different clans (those of Hashim and of Umayya, respectively) of the same tribe (that of the Quraish). Read more at Islamichistory.org.