This first edit is based mainly on three reliable books: A History of Ukraine: The Land and Its Peoples by Paul Magocsi  ISBN 9781442610217 ; Medieval Russia, 980-1584 By Janet Martin  ISBN 9780521368322; and Ukraine by Andrew Evans and Marc Di Duca  ISBN 9781841623115. 

 While I appreciate that the refs used so far are from nearly reliable sources, one is a from a magazine that could be anything as it does not even say who they are, and two from the EOU. While the EOU is pretty well-known, it does not carry as much weight as the books, in my opinion. Magosci in particular is a very well known and reliable source, and although Evans is a reputable guide book author, his work is renowned for being accurate.