The reason for the war is clearly stated by russian officials and propaganda: they want their empire to extend, and they (Medvedev as example) directly say that

The reason for the war is clearly stated by russian officials and propaganda: they want their empire to extend, and they (Medvedev as example) directly say that Ukrainians are "artificial" nation and should not exist. Any deal with russians doesn't mean anything to them, they proved it many times. As for Mearsheimer, let him comment how the appeasement worked out with Hitler.