Ukraine IS Russia. When Peter I conquered Russia, it appended "Emperor of Russia" (Царь всея Русси) to his title. Ukraine IS the Russian state. Russians call themselves "Russish" (русские), and their country Rossiia (Россия), to distinguish themselves from Russians (русичи, русины) and Russia (Русся, Русь)
Well it looks that you are not Russian, your word analysis is quite wrong. We call ourselves русские(Russians) to distinguish ourselves from россияне(citizens of Russia).
It's meaningless to look at maps of Ukraine in 1919-1920, because it was failed state at that time, born by total chaos brought by Bolshevik's rebellion and defeat in WWI, caused by it. Also Crimea was not a part of Ukraine even then, they had their very own independent republic.
Ukrainians considered Russians in the Empire, at least those who lived on the left bank of Dnieper.
Ukraine Republic was failed because of invasion. It's meaningless to talk with aggressor.
BTW: can you explain meaning of "scratch Russish and you will find Tatar/поскреби русского и найдёш татарина"? WTF is "russificated peoples/обрусевшие народы"?
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.
Crimea and Cuban were part of Ukraine prior to soviet invasion. Look at maps of Ukraine in 1919-1920: https://en.wikipedia.org/wiki/Ukrainian_People%27s_Republic .