A Little Bit of History.
1610-1612. So called Times of Trouble in Russia. Poles (and Lithuanians) invade Russia (through the territories of the modern Ukraine, obviously), capture Moscow, and install their puppet, so called, False Dmitry. Two years of misrule, cases of cannibalism reported.
1709. Swedish King, Charles XII, fighting Peter the Great, failed to conquer Russia from the north and decided to invade through the southern lands. He convinced Ukrainian Hetman, Mazepa, to join him. Decisive battle was fought at Poltava (the heart of today's Ukraine).
1812 French invade Russia (marching through the same "Ukrainian Route." Moscow burned down, desecrated and robbed again.
1914-1920. WWI, Russian Revolution, Civil War. Germans who more or less forced Ukraine into existence, took over Kiev, which changed hands 19 times within this period; Russian-Polish war followed the revolution. Again, modern Ukraine is the battlefield, with plenty of civilians killed including Jews, some newspapers actually used the term "shoah" to describe their plight as the result of all the violence.
1941. WWII. Germans again, and again they march into Russia through Kiev, murdering everything on their way. German forces were as close as 19 miles from the center of Moscow.
And of course, this century mess, both in 2014 and now.
In other words, at least for the last four hundred years, at the beginning of every century, there is trouble or invasion on Ukrainian border.
That's the context of Russian sensitivities and anxieties about this territory. We are all sensitive to Polish or Baltic anxieties and their fear of Russian invasion. Same sensitivity should be applied evenly to all sides.
These historic facts are not justification of anything nor are they condoning of anything. But they do provide a rather relevant context to explain the behavior of anyone who is triggered by the history of previous traumas. Think of Israel, and how its historical traumas are always used to explain its aggressive behavior.