Origins of the Seljuks
The Seljuks were a large and powerful tribe of Turks from present day Turkmenistan.
The Sultanate of Great Seljuk
In 1054 the Seljuk Turks ventured to intrude onto Ummayad territory. It was no accident, they came with a purpose, to conquer the entire Near East and the world beyond. The forces the Ummayad governor of Uzbekistan sent to eject them was outmanouvered and annihilated. All of Uzbekistan, and later Afghanistan, at the Battle of Kabul, was forfeit - as was the Principality of Merv, though no one, residents included, was too sorry to see it go. The Seljuks were so impressed by Merv that they made it their capital. They were markedly less impressed with the performance of their rivals, and overwhelmed them so completely at Tabriz, that the Ummayad Caliph, Mahdiq, signed a definitive peace, effectively signing away all of his territories in return for the preservation of his spiritual authority. The Seljuks, who were hardly losing out, accepted peace on this basis; by 1060 they had consolidated most of the former Ummayad area under their control.
Conflict with the Byzantines
In 1070 a Byzantine army from Antioch invaded Armenia. The newly formed Sultanate of Great Seljuk took this as a threat and in 1071 they attacked the Byzantines at Manzikert near Lake Van in Armenia. The result was a surprising smash victory for the Turks. The Byzantines, reeling from this humiliating defeat, were forced to retreat far into Anatolia and draw deep into their reserves of soldiers from the Balkans. They decided to fight one last battle for Anatolia near Dorylaeum. With fresh troops entrenched in strong defensive positions the Byzantines threw back every Seljuk attempt to dislodge them and continue their advance towards Constantinople. After two days of fruitless assaults the Turks settled for a peace with the Byzantines in which they received Armenia for their victory at Manzikert.
Decline and Disintegration
Around 1090 problems began to arise over succession. The Sultan had four sons who all wanted to succeed him. Between 1094 and 1097 a civil war raged that crippled the Seljuks' military potential for further conquests. After the war's conclusion, areas of their vast empire starting declaring independence under Emirs and Atabegs. Over the next 100 years, the Empire of Great Seljuk gradually disintegrated, eventually being absorbed in the east by the Khwarezmids and their lands in the west going back to the now defunct Ummayad Caliphate.