All the Rus countries used to belong to the Kievan Rus empire centred on Kiev. Kiev was a major city from at least the 6th century, while Moscow was just a lightly inhabited swamp area! Kiev reached its peak in the 10-12 centuries and declined after a Mongol invasion in 1240.
The Dnieper River area in Ukraine is where the famous horse riding warriors the Cossacks originated. Russia used them as the soldiers of choice after Catherine the Great's annexed Ukraine, where they are much better fighters to this day than any Russians.
Ukraine has never been comfortable under anybody elses rule and has always fought against this. Being a major crossing point in Europe where "Ukraine" means borderlands they have been under various empires at various times, The west of the country, predominantly under central European empires and the East more Russian and the South, Crimea had a strong Ottoman influence with their Tartar population.
There was much conflict between the Ukrainian people and the Soviet authorities, especially Stalin, who after a 1930 'Maiden' against Soviet authority forced many to move to other Russian areas, to Gulags or forced labour camps and killed between 5-8 million Ukrainian people. About 5% of the current Russian population are of Ukrainian descent.
In Soviet time much of Russian Industry and their scientific base was in Ukraine, where they are a clever industrious people. They currently have the 4th best educated workforce in the world. Since 1991 they have struggled where they have a similar Russian influenced Kleptocracy but with a semi-functioning democracy, freedom of speech and press freedom. Yanukovych tried to go the absolute rule, Putin route, and failed. A good lesson to any politician who pulls up the drawbridge after being elected, thinking that democracy belongs to them! The Euro-Maiden showed, yet again, it belongs to the people and a country's political leaders are only in charge where the people have given their consent.
Where Putin has made many major blunders since 1999 and his regime is heading for the sunset, but as a ruthless KGB operator, he won't go quietly. The Nemtsov murder was it Kremlin state terror, the current Kremlin nationalist hate campaign, or chaos where the Kremlin is losing control?