This is a good analysis from LSE of Ukraines legitimacy and Russian spin on claims to the region.
The notion that Ukraine is not a country, but a historical part of Russia, appears to be deeply ingrained in the minds of Russian leadership.
blogs.lse.ac.uk
A pretty accurate analysis of the situation - I'd add that the two periods during Stalin's rule either side if the war further complicated it as it massively altered the demographic make up by effectively turning the Cossack population from the dominant ethic group to a small minority - kind of creating the vacuum then filled in the east by ethnic Russians and in the west by ethnic poles and other nearby states - borders drawn, redrawn, periods of mdny years where part of the country was defacto Russian/Polish/Other controlled.
Not quite as bad as the old Yugoslavia in terms of its issues - but was a powder keg nonetheless.
If this entire thing hadn't occured the best solution would have been a country divided into the better part of Ukraine and a seperate semi independant east with a degree of autonomy but with it's charter including prohibition of ever joining the RF, so a true autonomy not a facade of one.
Since 91 the demographic of the country in every election has shown just how divided the east / west are in pretty much irreconcilable ways. (Pro Russian leaders crapped on the west population west crapped on the eastern population).
Throw on top of that endemic corruption, the undeniable outside interference from Russia and the US for over 30 years in pretty much every government they've had and dunno if the country had a genuine chance to prosper as a truly independant nation.