Ukraine has long been run by very corrupt politicians and oligarchs, who happen to be very friendly with the people responsible for trying to usher in the NWO. USA has a particular interest in defending Ukraine (verbally) at the moment, because the majority of the head democrats, including the "POTUS" and his son, the Pelosi's, Kerry, Obamas, Schiff, and RINO Romney have made millions off of giving US taxpayers aid to Ukraine and then being reimbursed that aid back, or laundering money through gas company shells. Not to mention, they are all owned by Soros who is heavily invested into the money laundering portions of Ukraine.
Putin and Trump are on the same page with taking down the NWO, and its likely that this "military operation" is the culmination of that in this country. Think Afghanistan ushering in new government and flushing out old. Think Saudi Arabian roundup at the Ritz.
One country at a time. But the media can't admit this because they're bought and paid for as much as the politicians are.
It goes deeper, but thats the surface level explanation.