For this achievement you'll need to control three specific cities. This achievement can be obtained in both the Eye of the Vortex campaign and Mortal Empires campaign.
The three cities, Pox Marsh, the Awakening, and the Blood Swamps, are in both campaigns part of The Vampire Coast region, as part of Lustria. In both campaigns the cities are a swamp and occupied by the Vampire Coast faction of Luthor Harkon. In the Eye of the Vortex campaign The Star Tower is also part of this region, but is not needed for the achievement.
As any faction, occupy all three cities and the achievement should unlock.