'Remnants of finno-ugric population'?
Afaik, varyags didnt commit no genocide, and slavic population wasnt finno-ugric, although these were present as well. ))
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Having browsed some sources - yes, it should be classified as conquest. Though Rurik was invited by Novgorod to become a Knyaz/Prince, his son Oleg waged a military campaign, unifying the eastern slavs under his rule.
Its just that nobody now perceives him as an outlander; historians refer to him as of a great Russian prince.