The Azerbaijanis or Azeris (; , آذربایجانلیلار) are the Turkic-speaking ethnic group living mainly in the Republic of Azerbaijan and in Iran (especially in Iranian Azerbaijan), as well as in neighboring states. Commonly referred to as Azeris/Āzarīs (آذری – Azəri) or “Azeri Turks” (Azəri türkləri) they live in a wider area from the Caucasus to the Iranian plateau. The Azeris are predominantly Shi’a Muslim and have a mixed cultural heritage including Iranian, Turkic and Caucasian elements. Following the Russo-Persian Wars of 1813 and 1828, the territories of the Qajar Empire in the Caucasus were ceded to the Russian Empire and the treaties of Gulistan in 1813 and Turkmenchay in 1828 finalized the borders between Czarist Russia and Qajar Iran. The formation of the Azerbaijan Democratic Republic in 1918 established the territory of the Republic of Azerbaijan. Despite living on two sides of an international border, the Azeris form a single ethnic group. However, northerners and southerners differ due to nearly two centuries of separate social evolution of Iranian Azerbaijanis and Azerbaijanis in Russian/Soviet-influenced Azerbaijan. The Azerbaijani language unifies Azeris, and is mutually intelligible with Turkmen, Qashqai, Gagauz, Turkish, and the dialects spoken by the Iraqi Turkmen, all of which belong to the Oghuz, or Western, group of Turkic languages.