Putin didn’t carve off the eastern parts of the country, although he could have. I now infer he wishes to take the whole thing. There are sometimes reasons why you do not wish to stop and take the free lunch and create a focal line, namely that it can constrain you for the future. I don’t mean that Putin will conquer Ukraine by military force, but rather bit by bit he will harass the current government into losing legitimacy, until a strongly pro-Russian, pro-Putin government is running that country. By hook or by crook.