Ethnic cleansings in those territories are a fabricated casus beli for Russia 'green man'. There were tensions between Russian and Ukrainian nationals in those territories, but I've seen no data on large scale extermination operations.
Ukraine engaged in a defensive war with a force clearly backed by their stronger neighbor that just laid claim to another piece of their land (Crimea). This was a land grab in all but name, no matter how much propaganda tries to paint it as a legitimate independence movement. Blame for casualties of that war lies entirely on separatists and Russia.