Uzbek belongs to the Eastern Turkic, or Karluk, branch of the Turkic language family. External influences include Persian, Arabic and Russian. One of the most noticeable distinctions of Uzbek from other Turkic languages is the rounding of the vowel /a/ to /ɒ/, a feature that was influenced by Persian.
Turkic speakers probably settled the Amu Darya, Syr Darya and Zarafshan river basins since at least 600–700 CE, gradually ousting or assimilating the speakers of Eastern Iranian languages who previously inhabited Sogdia, Bactria and Khwarezm. The first Turkic dynasty in the region was that of the Kara-Khanid Khanate in the 9th–12th centuries, who were a confederation of Karluks, Chigils, Yaghma and other tribes.
Uzbek can be considered the direct descendant or a later form of Chagatai, the language of great Turkic Central Asian literary development in the realm of Chagatai Khan, Timur (Tamerlane), and the Timurid dynasty (including the early Mughal rulers of India). The language was championed by Ali-Shir Nava'i in the 15th and 16th centuries. Nava'i was the greatest representative of Chagatai language literature. He significantly contributed to the development of the Chagatai language and its direct descendant Uzbek and is widely considered to be the founder of Uzbek literature. Ultimately based on the Karluk variant of the Turkic languages, Chagatai contained large numbers of Persian and Arabic loanwords. By the 19th century it was rarely used for literary composition, but disappeared only in the early 20th century.
The term Uzbek as applied to language has meant different things at different times. Prior to 1921 "Uzbek" and "Sart" were considered to be different dialects: