Excerpts from Books and Wikipedia
"In about 1038, a group of nomadic Turkish tribes dominated by the Seljuks swept out of Central Asia. In 1055 they occupied Baghdad and went on the conquer Armenia. Alarmed by the approaching threat, the Byzantines marched east from Constantinople under Emperor Romanus Diogenes, but they suffered a crushing defeat at Manzikert in 1071. This drove the Byzantines out of Asia Minor and ultimately provoked the Crusades." [DK Timelines, p. 174] "It is the Battle of Manzikert, fought near Lake Van in Armenia [near today's Malazgirt in Turkey] in 1071 in which the Byzantines, under the Emperor Romanus IV Diogenes, were defeated by the Seljuk Turks, led by the Sultan Alp-Arslan. . . This Byzantine defeat ushered in an age of Sunni Muslim Turkish conquest, that had its finale in the equally Sunni Muslim capture of Constantinople by Ottoman Turks in 1453, and the end of the 1,100-year-old East Roman Empire, begun by Constantine himself back in the fourth century AD. The last event in this historical chain was the expulsion of the last ethnic Greeks from Asia Minor in 1922. [Catherwood: The Middle East, p. 95-7]