Because the current ethnic tensions that showed up shortly after Putin's buddy was removed by his own Parliament are indicative of how the Ukraine has functioned for the last 23 years as an independent nation?
Those borders have been accepted for over 100 years, by all parties, including Russia. They have a better "historical basis" then say the present borders of Poland, Germany and this completely artificial Russian province of Kalingrad. There are very few if any states on this planet that are drawn on 100% ethnic lines! or even historical ones.
These places have been Ukrainian for about 100 years.
Except that the border has been in its present form since the reincorporation of the Ukraine into the USSR and the borders were guaranteed in their present form in a 1994 treaty signed by Russia.
Let us have a look at the history of some of the major cities in eastern and southern Ukraine.
Kharkov - founded in 1654 by soldiers sent from Moscow, on uninhabited land known as the "dikoe pole", or "wild field". Some of the settlers were Ukrainians from west of the Dnepr, who were fleeing the fighting there. From its foundation, Kharkov always was part of Muscovy, and then the Russian Empire.
Odessa - founded in 1792 by order of the Russian Empress Catherine II, on territory conquered from the Ottoman Empire. The earliest settlers were Moldavians, who became russified. No Ukrainians had ever lived in the area where Odessa was founded, or indeed anywhere else on the Black Sea coast. Thus Odessa was from the very beginning a Russian foundation, not a Ukrainian one.
Sevastopol - founded in 1783 by order of the Russian Empress Catherine II, on the territory of the annexed Crimean Khanate, a vassal state of the Ottoman Empire. The indigenous people were Crimean Tatars; no Ukrainians had ever lived there. Thus Sevastopol was from its very beginning a Russian foundation, not a Ukrainian one.
Dnipropetrovsk - first founded in 1635 as the Polish fortress of Kodak, built in the "dikoe pole", on the border between Polish territory and that of the Crimean Khanate. The first settlers were Ukrainian Cossacks, placed there by the Polish Government as border guards. thus, the town was originally Ukrainian although not part of Ukrainian ancestral territory, since the indigenous inhabitants were nomadic Kipchaks. The territory around Kodak was ceded by Poland to Muscovy in 1654 under the Treaty of Pereiaslav, and in the 1760s a Zaporozhian Cossack village called Polovytsia was established. The modern city was founded in 1776 by Prince Grigorii Potemkin, the governor of New Russia, the territory newly conquered from the Ottoman Empire, and was moved to its present location near Polovytsia in 1783.
Thus, this city was originally a Polish-Ukrainian foundation, but became Russian, due to the settlement of large numbers of Russian colonists in the 19th Century.
Donetsk - founded in 1869 by the Welsh businessman John Hughes, who built a steel plant and several coal mines in the area. It is situated in the steppe region, which at the time was largely uninhabited; no Ukrainians had ever lived in that region throughout history. The population consists mainly of Russian colonists from the north, who settled the area in the late 19th and early 20th Centuries. Thus Donetsk was from its foundation a Russian city and has never been ethnically or historically Ukrainian.
Lugansk - founded in 1795 by the British industrialist Charles Gascoigne, who built a metal factory there. Like Donestsk it was situated on largely uninhabited steppe land, and was settled by Russians coming from the north. Thus, Lugansk. like Donetsk, was from its foundation a Russian city, and has never been ethnically or historically Ukrainian.
Donetsk and Lugansk are ethnically and historically the least Ukrainian and most Russian cities in the polity called "Ukraine".
The above cities may be compared with Kiev, an ancient city that has been Ruthenian or Ukrainian since the 9th Century, and Lviv, situated in the ancestral heartland of the Ukrainian people, founded in 1240 by King Daniel of Halych, a Ruthenian prince of the Rurikid Dynasty. Thus, both Kiev and Lviv have been ethnically and historically Ukrainian since the very beginning of their recorded history.
If the present Ukraine were to be divided, with some areas going to Russia and the remainder continuing to exist as an independent state of the Ukrainian people, then Odessa, Sevastopol, Donetsk and Lugansk should certainly go to Russia. Kharkov and Dnepropetrovsk might go to Russia or remain with Ukraine, depending on the wishes of their inhabitants; either way, their future would be as border cities, on a new Russian-Ukrainian frontier corresponding to ethnic and historical realities.
Except that the border has been in its present form since the reincorporation of the Ukraine into the USSR and the borders were guaranteed in their present form in a 1994 treaty signed by Russia.
The present issue is the "territorial integrity" of Ukraine, and I see no reason why that should be regarded as sacrosanct. There have been many cases in modern history of states being compelled to surrender part of their territory, eg Serbia was compelled by NATO to surrender Kosovo. And decades before that Britain allowed Ireland to break away.
The provinces of Donetsk and Lugansk in particular are historically and ethnically Russian; there is no ethnic or historical reason for their remaining part of Ukraine rather than being transferred to Russia.
If the new rulers of Ukraine, who seized power by violence, are wise, they will allow the parts of Ukraine that are not ethnically or historically Ukrainian to secede peacefully, if that is what the populations of those parts want, and rest content with ruling over the historical heartland of the Ukrainian people, the region west of the Dnepr.
The problem is that the new rulers of Ukraine are not wise; they are nationalist extremists, motivated by a 19th Century ideology of hatred for the "Muscovites".