OK, the thread on Russian colonies in Africa got me thinkin- how could there have been created in Russia from say Ottoman times, a substantial population of Afro-Russians- say, if the experience of Peter Gannbial being sent from Ethiopia/Eritrea to St Petersburg was repeated many times over ? There have been a greater no. of black ppl in Russia during the 20th C, such as with African-Mmerican Communists & their descendants who ended up moving to the USSR during the 1930s, & black Africans from Marxist countries who came over to study from the 1960s, marrying local Russian wives- but WI there'd been a much bigger black Russian population well before then ?
Check out this interesting article
http://articles.latimes.com/1999/jun/13/news/mn-46201
At the risk of causing controversey african and black are not synonomous, the main ethnic groups of Ethiopia are not what we would call black africans.
That aside it is an interesting (or do I mean odd) challenge.
If it was Britain or France it would be easy, but Russia without her colonialism is pushing it. Maybe the Russians, motivated by religion, stories of prester John and vague knowledge of Christian Ethiopia form, hire or piggyback on various expeditions finally sending diplomats, and missionaries to Ethiopia.
Perhaps they convert a large proportion of the population, including one branch of the royal line(s) that is later outcast and travels to Russia with their entourage (most likely with the help of another European power and not before wandering around Europe).
Maybe the Russians decide that the Ethiopians following an older Christian tradition are closer to Christ, and actively recruit Ethiopian priests to reform the Russian orthodox Church?
Maybe the main Ethiopian Priest gets a vision or an inducement and decides that Russia is to become the vehicle and champion of Christianity and so relocates the ark of the covenant (which they still believe they have) to Moscow along with several hundred Priests and hangers on.
It is all seems mighty tenuous though.