Your challenge, should you choose to accept it, is to have a monotheistic faith emerge from Slavic paganism sometime between the Fall of Rome in 476 and the Christianisation of Russia. Said faith must unite the East Slavic peoples AT LEAST, expand rapidly during the Dark Ages and Medieval Era, and it must be a majority religion in Slavic territories to the present day. It does NOT have to be derived from the Judeo-Christian tradition.
OTL Islam MAY exist.
Bonus points for a detailed scenario, EXTRA bonus points for a short or full TL.
OTL Islam MAY exist.
Bonus points for a detailed scenario, EXTRA bonus points for a short or full TL.