
Un-named country: Send troops into a neighbor, steadfastly denying they have any troops there.
Rest of world: Sits around for weeks and then says, "Oh, you shouldn't do that."
Un-named country: Negotiates a cease fire after securing a good amount of territory.
Rest of world: Sits around relieved that we have a cease fire. Everything is better now.
Un-named country: Moves more troops into to its newly acquired territory. Makes sure cease fire disintegrates. Moves troops into more territory.
Rest of world: Sits around for weeks and then says, "Oh, you really shouldn't do that."
Un-named country: Negotiates a cease fire after securing a good amount more territory, knowing that in round three they'll be able to secure a nice solid land corridor before winter.
That's the point here, secure the land corridor without much fuss and muss, before winter. Why? The last bit of land that was successfully annexed is going to be a helluva costly bit to supply and not provide a whole lot of benefit otherwise. It's easy to accomplish if you can take a break to bring up supplies and reinforcements along the way.
NATO you don't have to send troops. You don't have to send offensive weapons. Send warm clothing, flak jackets, and short range anti-tank missiles. They won't be of any use to anyone shooting down airliners or invading other countries, but they sure as hell will make an armor column think twice about advancing. Hell, for cover you could even sell it at the nice price of $1 per.