What are the main religions and beliefs mentioned in the text about the Middle Volga region?

Main Religions and Beliefs:

• Islam (professed by ancestors of Tatars and Bashkirs)
• Paganism (professed by Mari, Udmurts, Mordvins, and Turkic Chuvash, believing in multiple gods)
• Orthodoxy (introduced with the arrival of Russian settlers and the Christianization of local residents after the Kazan Khanate joined the Moscow state)

Answer: The main religions and beliefs mentioned are Islam, Paganism, and Orthodoxy.