Currrents stats show that as the two main ethnic groups: Ukrainian: 77% Russian: 17%
Ukraine's problems with Russia are not cut and dry. Even back in the 1700s, the Russian empire had annexed most of the Ukraine's landmass for its own use. After WW2, Russia seized it as a spoil of war, installed full communist leadership throughout, and maintained a culture of "Russification" for decades. Many ethnic russians migrated there during the cold war period. Ukraine was one of the breadbaskets for the USSR with large state run farms. Many large factories were built. It also held a massive military strategic value for Russia. Many military bases and nuclear missile sites were located there.
Russia still fights to maintain Ukraine as part of its "sphere of influence". The key being the Russian navy's black sea port located in the city of Sevastopol in the Crimea region. Ukraine only became an independant country in 1991, but considering all the ethnic russians still living in the eastern and southern parts, Russia still wants to have as much political and economic control as possible over it. Russia looks upon Crimea the same way they look up Georgia. That its land that belongs to them, even if the borders say otherwise. Russia is paranoid that if Ukraine politically and culturally aligns itself with NATO and the US, that they will lose the power of a perpetual lease on Sevastopol.
Thus Russia plays games like issuing passports to anyone in the Crimea region so they can claim they are all Russian citizens living there and in need their protection.
Thus Russia also will go to any lengths, including political assasinations, to maintain its control over the Ukraine.
Take a look at electoral map of Ukraine. The part of Ukraine which was for centuries a part of the Commonwealth (Poland & Lithuania) votes for native Ukrainians, either Yushchenko or Tymoszenko. The parts that were never within Poland votes for Russians.
This means only one. Ukrainian heritage and consciousness didn't survive under Russia and this speaks for itself, unfortunately.