Russia has risen to military prominence as it breaches international law and violates international sovereignty. The prospect of the US Government providing arms to the Kiev government will render Ukraine a buffer state between two super powers. Russia, as the Soviet Union, is again engaging in zero sum international relations and strengthening its position to the detriment of weaker states.
Historically, on the other hand, the precedent demonstrates a strong connection between Ukraine and Russia. For 300 years Ukraine was part of Russia. Furthermore the independence of Ukraine was to an extent forcibly enacted by the United States, arbitrarily divided in the wake of the Soviet Empire.
Politically after the rise up against the president Viktor Yanukovych there has been a rise in the general disapproval of the government. It feels that since Viktor’s abdication from the role of president the approval of the government has continued to slide and political unity has fallen apart. Currently many Ukrainians think that the government is illegitimate but only a small minority want to unite with Russia.
Obvious Russian military aid to East Ukrainian rebels has little to no legitimacy within Ukraine. The rebel group is leaching off the poor ratings of the incumbant government and are attempting to rouse further discord. Unilateral American aid against rebels in Ukraine is legally acceptable but on the other hand it send a signal to Russia that again they are threatened on their doorstep again, and will in all probability give Putin more legitimacy to feed troops and arms to Ukrainian rebel groups.