The west only ever had one giant realm, and that was Astrum. Possibly Caerwyn before the crusade that destroyed it. After that was Kabrinskia/Farronite Republic, Asylon, and Niselur that had to fight together just to match Astrum.
Realm size wise, Astrum was the largest. Noble count wise it was actually Asylon and Barca. At least in the west. I think in the east, it was Luria Nova.
