The Seljuq Turks defeat the Byzantine army at the Battle of Manzikert, and soon gain control of most of Anatolia.

The Battle of Manzikert or Battle of Malazgirt was fought between the Byzantine Empire and the Seljuk Empire on 26 August 1071 near Manzikert, theme of Iberia (modern Malazgirt in Mu Province, Turkey). The decisive defeat of the Byzantine army and the capture of the Emperor Romanos IV Diogenes played an important role in undermining Byzantine authority in Anatolia and Armenia, and allowed for the gradual Turkification of Anatolia. Many of the Turks, who had been travelling westward during the 11th century, saw the victory at Manzikert as an entrance to Asia Minor.The brunt of the battle was borne by the Byzantine army's professional soldiers from the eastern and western tagmata, as large numbers of mercenaries and Anatolian levies fled early and survived the battle. The fallout from Manzikert was disastrous for the Byzantines, resulting in civil conflicts and an economic crisis that severely weakened the Byzantine Empire's ability to adequately defend its borders. This led to the mass movement of Turks into central Anatoliaby 1080, an area of 78,000 square kilometres (30,000 sq mi) had been gained by the Seljuk Turks. It took three decades of internal strife before Alexius I (1081 to 1118) restored stability to Byzantium. Historian Thomas Asbridge says: "In 1071, the Seljuqs crushed an imperial army at the Battle of Manzikert (in eastern Asia Minor), and though historians no longer consider this to have been an utterly cataclysmic reversal for the Greeks, it still was a stinging setback." It was the first, and only, time in history a Byzantine emperor became the prisoner of a Muslim commander, and the first time since the emperor Valerian that a Roman emperor was captured alive by an enemy force.

The Seljuk dynasty, or Seljukids ( SEL-chuuk; Persian: آل سلجوق Al-e Saljuq, alternatively spelled as Seljuqs or Saljuqs), also known as Seljuk Turks, Seljuk Turkomans or the Saljuqids , was an Oghuz Turkic Sunni Muslim dynasty that gradually became Persianate and contributed to the Turco-Persian tradition in the medieval Middle East and Central Asia. The Seljuks established both the Seljuk Empire and the Sultanate of Rum, which at their heights stretched from Iran to Anatolia, and were targets of the First Crusade.