The name Turk was first used by the Chinese in the 6th cent. to designate a nomadic people who had established a large empire stretching from Mongolia to the Black Sea. This empire, which was divided into two independent parts, was forced to accept Chinese sovereignty in the 7th cent. The northern empire regained its independence in 682, and the oldest known Turkic inscriptions (see under Orkhon) are related to it. In succeeding centuries control of the area passed from the Oghuz Turks to the Uigurs and to the Kyrgyz, who were the last Turkic peoples to reside in Mongolia. They, like their predecessors, migrated to the south and west after they were expelled (924) by the Kitai. Other Turkic peoples, notably the Khazars, Cumans, and Pechenegs, played important roles in the medieval history of S Russia and SE Europe. The Turkish groups of the greatest import in the history of Europe and W Asia were, however, the Seljuks and the Osmanli or Ottoman Turks, both members of the Oghuz confederations. The Arab annexation of the area of ancient Sogdiana in the 7th cent. brought the Oghuz Turks into direct contact with the Abbasid caliphate and later with the Persian Empire. The Turks embraced the Sunni Muslim faith and began to migrate to the Middle East. At first they were used as mercenaries by the Abbasids, but soon the Turks became the actual rulers of the empire.

At the beginning of the 11th cent. a great wave of Seljuk Turks, led by Tughril Beg, conquered Khwarazm and Iran. They entered Baghdad in 1055; Tughril Beg was proclaimed sultan. Under his successor, Alp Arslan, the Seljuks conquered Georgia, Armenia, and much of Asia Minor, overran Syria, and defeated (1071) the Byzantine emperor Romanus IV at Manzikert, opening Byzantium (except for a small area around Constantinople) to Seljuk and Turkmen occupation. This irruption was a major factor in bringing about the Crusades, during which a three-part struggle among Christians, Seljuks, and Egyptian Mamluks developed. Alp Arslan's son, Malikshah (reigned 1072-92), ably administered and developed his huge empire; he was a protector of Omar Khayyam, who reformed the calendar at his behest. At the start of the 12th cent. the Seljuk empire began to fragment, and various parts achieved virtual independence. The attacks of the Khwarazm shah led to the final downfall of the empire in 1157.

Among the successor states were the Zangid sultanate of Syria, whose ruler Nur ad-Din was known for his victories over the Crusaders; the empire of Khwarazm, which at one time nearly attained the limits of the earlier Seljuk empire; and the sultanate of Rum or Iconium (see Konya), which comprised a large part of Asia Minor. All the Seljuk states were overrun in the 13th cent. by Jenghiz Khan and his successors, whose hordes comprised both Mongols and Turks and became generally known as Tatars. The Turko-Tatars now living in the nations of the Commonwealth of Independent States are largely descended from the Golden Horde of Batu Khan, as are the Uzbeks (see Uzbekistan), who ruled a vast empire in the 16th cent.

In Asia Minor the sultanate of Konya was taken over, after the Mongol wave had receded, by the emirate of Karamania (see Karaman), but the Osmanli Turks completed the overthrow of the Byzantine Empire. A minor tribe and the last of the Turkish invading peoples, the Osmanli had been assigned (13th cent.) to the border area of the Byzantine Empire by their Seljuk overlords. It was largely this position as guards of a constantly contested frontier that allowed them to develop their highly disciplined organization, which in turn enabled them in the 14th cent. to make themselves masters of the ruins of the Seljuk empire in Anatolia. Their first historic ruler Osman I, gave his name both to the nation and to the dynasty that ruled an empire extending, at one period, from Vienna to the Indian Ocean and from Tunis to the Caucasus (see Ottoman Empire). The people of modern Turkey, which was founded after the collapse of the Ottoman Empire in 1918, are called Osmanli Turks. The original Osmanlis had merged at an early stage with the Seljuks, and their descendants mixed extensively with Muslim converts from the many dozens of nationalities that made up their empire.