Invasion was succesful because people did not support the Ukrainian government and considered themselves Russian. Unfortunately they were betrayed by Bolsheviks

Invasion was succesful because people did not support the Ukrainian government and considered themselves Russian. Unfortunately they were betrayed by Bolsheviks then. About Russian and Tatar - the original usage of that phrase differs from current. It was used in 19 century to present Russia as some barbarian horde, not European country it was these days. I think the origins of the phrase was in the book "La Russie en 1839", which is basically a piece of anti-Russian propaganda of 19 century. Обрусевшие народы - ethnicities that lost(sometimes partially) their identities and now are considered Russians. Russia is actually a melting pot of quite different ethnicities, including mongoloid and slavic ones. For convenience some of these ethnicities are considered just Russians. Being Russian is not really an ethnic thing - it's more of cultural one.