Woburn is the second largest city taken by the Wyrm Legion, and the furthest south they have journeyed so far.
Derge is the site of the original landing of the Legion, and is effectively the command center of the invasion.
No organized military resistance has presented itself, but the Legion's maps and information are several centuries out of date, leaving them in control of a large swatch of land that they do not understand.
When the Dragonborn went on their self imposed exile over three hundred years ago, Derge was the seat of the most powerful empire in the north. When the Legion arrived, they found a city that was a shadow of its former self, home to a terrified population that put up no tangible resistance.