The Ukraine has strong historical links to Russia, and is considered perhaps the birthplace of Russia itself, with Kiev being the capital of the Medieval Kievan Rus empire. After the collapse of the Kievan Rus empire, the area was divided, occupied, fought over, by a variety of invaders: Poles, Lithuanians, Cossacks, Russians, Turks. This happened over many centuries until it was eventually subsumed by the Russian Empire, by and large, by the 18th century - but its territory was by no means fixed by that point.
Under the Russian Empire, a policy of assimilation and Russification occurred in Ukraine as it did throughout the empire. National identities were discouraged and even suppressed. With the advent of the 1917 revolution, the Communists vowed to correct the age-old oppression of the 100+ minority nationalities that existed within the Russian borders. They officially recognised equality and sovereignty of all the peoples of Russia; their right for self-determination, including secession or independence; freedom of religion; and free development of national minorities and ethnic groups on the territory of Russia. The first line of the Soviet National anthem celebrated this "unbreakable union of free-born republics"
However, as with everything else in the Soviet Union, such nominally positive policies were negated / upturned by the exigencies of power and the effecting (or effectuation if there is such a word) of communist dictatorship. Stalin subverted the nationalities policy by drawing up internal borders designed to create tensions between ethnic groups, ensuring there was always a local minority that would do Moscow's bidding in return for being protected by the Soviet centre.
The borders of these "independent" republics and "autonomous" regions did not often make sense in terms of their ethnic make-up, historic nationhood or cultural integrity. The leaders of the Soviet republics or autonomous regions were often a representative of the ethnic majority of that area, but their deputy would be an ethnic Russian and a higher ranking member of the communist party - to ensure the local leader did Moscow's bidding. The state apparatus and the hierarchy of the Communist Party were very closely linked. You couldn't rise through the ranks of the state bureaucracy unless you were a member of the Communist Party.
Paul Gole claims that this system worked only so long as there was coercion. He describes the structure as a "poison pill" - a description of business arrangements that make it difficult, if not dangerous, for anyone to try to takeover or even change the basic arrangements of another firm. In terms of the Soviet union, Gole contends, Stalin's system "ensured that anyone who sought to dismantle his totalitarianism would have to cope with ethnic anger and borders that guaranteed it would likely get worse".
Following the collapse of the Soviet Union, the Soviet republics became independent nations - preserving their the Soviet-defined borders and ethnic composition. As we have seen with Georgia and now with Ukraine, where a sizeable ethnic minorities exist, tensions have risen (and been exploited) through ethnic divisions leading to fault lines in the territorial integrity of these nations.