The North Greece Demilitarized Zone is established
Winter, 1957 A.D.: The quick mobilization of Norse submarines sinks more than half of the Greek Northern fleet, breaking the blockade at Helsinki decisively. England announces to the world that it is denouncing Greece, indirectly supporting the NAPA nations.
1958 A.D.: Elis is besieged with the aid of fresh Norse artillery, beginning the smaller and more focused Operation Firebrand.
One of the reasons Operation Firestorm failed was that I tried to attack too many things at once. Firebrand will focus all of my strength on one city at a time, assuring quick victories.
Greece sends a bunch of outdated militiamen that can't really fit under the Norse definition of a "military" to relieve Elis.
Greece is still being considerate enough to provide the comic relief in this brutal war, repeatedly attacking my modern units with guys on horses and other outdated crap. They have more than enough money to be upgrading them, so I can only really chalk it up to arrogance.
Summer, 1959 A.D.: The Greek militias are dead almost to a man, but more reinforcements (now armed with assault rifles) approach the Norse lines from the Southwest.
We're now neck and neck in infantry tech, but my superior artillery and air power should more than make the difference.
Artillery fire keeps the fresh Greek infantry pinned down, and Elis is captured by Norse forces before they can arrive. All Greek government officials are ousted, and much of the town's infrastructure is dismantled. It is put in the hands of a local, Greek-born governor, and becomes the first territory to fall under the North Greece Demilitarized Zone (NGDMZ) designation.
Which is to say, I burnt it down. I don't really want these little cannon fodder cities on my border. They aren't worth many resources and will just weigh down my Happiness rating. So, poof they go. This being the modern era; and I being a just ruler, I'm rationalizing this in the fiction as me creating a demilitarized zone on the Greek border. Which is, essentially, the point of this entire campaign.