You mean when the democratically elected parliament removed Yanukovych from office after he conspired with the Russians and then fled the country? Even if it were as you have characterized it, it would have been no threat to Russia. You also conveniently ignore the fact that there were two (2) national elections afterwards and that the present government was freely elected, not "installed."
Neither was waging war on disenfranchised voters who wanted to secede in Donetsk and Luhansk.
They were not disenfranchised. They could have freely participated in the following two elections if it were not for the Russian military occupation. Nor did the populations there, which are majority Ukrainian, seek to secede. Even in the Russian controlled "referenda" the vote was only for autonomy in a united Ukraine.