Center Army Group aka Army Group 'Center' were Nilfgaardian troops during the Northern Wars under the command of Field Marshal Menno Coehoorn. Its single most important task - to take Temeria, pushing the border of the empire as far north as the Pontar and hold that position. To accomplish this task, the support of two other flanking armed groups was required: the East Army Group and the Verden Operations Group. Of the two, the East Army Group had the more difficult mission. The original plan was unsuccessful, the Center Group being defeated at the Battle of Brenna.
The Center Army Group eventually ended up camped in southeastern Velen under command of Tavar Eggebracht and Field Marshal Havart var Moehoen during the times of The Witcher 3. It was either destroyed by the Redanian army under either Dijkstra or Radovid V or retreated back to Nilfgaard after the Temerians reclaim their country as a vassal of the Nilfgaardian empire.