Turks, Azerbaijanis and Turkmen all trace their roots to one steppe confederation
Their name simply meant tribe in Common Turkic. From the steppes north of Lake Balkhash, Oghuz herders rode west, converted to Islam and became empire-builders. Their descendants founded the Seljuk and Ottoman states, served in armies as far away as Morocco and Spain, and live on today as Turks, Azerbaijanis and Turkmen.
The Oghuz were a western Turkic people who formed a tribal confederation in Central Asia in the 8th century, conventionally called the Oghuz Yabgu State. After clashing with the Karluk allies of the Uyghurs, they moved west from the Jetisu region, and in the 9th century pushed the Pechenegs out of the lands around the Emba and Ural rivers. By the 10th century they grazed the steppes of modern Kazakhstan. The Arab traveller Ibn Fadlan described them as nomads who also grew crops, living a semi-pastoral life in felt-covered yurts.
Language offers one thread through the story. The Oghuz branch is part of the Common Turkic family, and the 11th-century scholar Mahmud al-Kashgari judged it the simplest of the Turkic tongues. Byzantine writers called them Uzes. As most Oghuz embraced Islam, Islamic sources began calling the Muslim ones Turkmens by the 10th century, and by the 13th century the older name had largely vanished. Earlier they had followed a Tengrist religion, raising carved wooden funerary statues ringed by stone balbals.
The 11th century split the Oghuz world. The Seljuk clan entered Persia and founded the Great Seljuk Empire. Another group, still Tengrist and known as Torks, broke Pecheneg dominance on the Russian frontier and was gradually Slavicised. Others, pressed by the Kipchaks, crossed the lower Danube into the Balkans, where a plague halted them and survivors became Byzantine mercenaries in 1065.
Their military edge came from mobility honed over centuries of herding, while kinship and marriage alliances held society together. After the Seljuks fell, the Ottoman dynasty conquered Anatolia in the late 13th century with a largely Oghuz army; legend traced its founder Osman back to Oghuz Khagan, the mythical ancestor of the Turks. Later Persian dynasties such as the Afsharids and Qajars, and the Aq Qoyunlu confederation, are thought to spring from Oghuz tribes too. The epic Book of Dede Korkut preserves echoes of 9th- and 10th-century Oghuz life, though it was probably written down much later.
Source: Oghuz Turks