Turkic languages
Pre-history

The homeland of the Turkic peoples and their language is suggested to be somewhere between the Transcaspian steppe and Northeastern Asia (Manchuria), with genetic evidence pointing to the region near South Siberia and Mongolia as the "Inner Asian Homeland" of the Turkic ethnicity. Similarly several linguists, including Juha Janhunen, Roger Blench and Matthew Spriggs, suggest that modern-day Mongolia is the homeland of the early Turkic language. Relying on Proto-Turkic lexical items about the climate, topography, flora, fauna, people's modes of subsistence, Turkologist Peter Benjamin Golden locates the Proto-Turkic Urheimat in the southern, taiga-steppe zone of the Sayan - Altay region.

Extensive contact took place between Proto-Turks and Proto-Mongols approximately during the first millennium BC; the shared cultural tradition between the two Eurasian nomadic groups is called the " Turco-Mongol " tradition. The two groups shared a similar religion system, Tengrism, and there exists a multitude of evident loanwords between Turkic languages and Mongolic languages. Although the loans were bidirectional, today Turkic loanwords constitute the largest foreign component in Mongolian vocabulary.

Italian historian and philologist Igor de Rachewiltz noted a significant distinction of the Chuvash language from other Turkic languages. According to him, the Chuvash language does not share certain common characteristics with Turkic languages to such a degree that some scholars consider it an independent Chuvash family similar to Uralic and Turkic languages. Turkic classification of Chuvash was seen as a compromise solution for the classification purposes.

Some lexical and extensive typological similarities between Turkic and the nearby Tungusic and Mongolic families, as well as the Korean and Japonic families has in more recent years been instead attributed to prehistoric contact amongst the group, sometimes referred to as the Northeast Asian sprachbund. A more recent (circa first millennium BC) contact between "core Altaic" (Turkic, Mongolic, and Tungusic) is distinguished from this, due to the existence of definitive common words that appear to have been mostly borrowed from Turkic into Mongolic, and later from Mongolic into Tungusic, as Turkic borrowings into Mongolic significantly outnumber Mongolic borrowings into Turkic, and Turkic and Tungusic do not share any words that do not also exist in Mongolic.

Turkic languages also show some Chinese loanwords that point to early contact during the time of Proto-Turkic.
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