it's getting quite tiring to discuss that it's all started with illegal coup sponsored by the USA in 2014
or we can go to 1991 and mention illegal separation from russia
anyway no matter how you slice it - current people in power in ukraine since 2014 killed russians in eastern ukraine which russia patiently asked them to stop doing for 8 years and those people keep power illegally and russia has full right to remove them
what russia is responsible is what notagain said above - they are guilty because they didn't crush it fast with full force which caused huge human loss and complete devastation in ukraine
So in 1991 Ukraine did not separate from Russia, it left the USSR. In 2014 the Ukrainians overthrew their Kremlin puppet of a leader over his rejection of opening free trade with the EU. The only coup that happened in 2014 was throwing out the Russians from Ukrainian government.