Sure, it was Oligarch, Perdan, Avamar, Rancagua vs Sirion, Fontan, Old Rancagua + Eleador on both sides at different times from what I remember but you cannot exclude everything that is a part of a larger war. There is almost never one versus one in bm.
Speaking of dead realms, since I have at times been paused, how did Old Rancagua die? Who killed Fontan? Who killed the realms on the islands that existed previous to OI (I think I missed one..like Kalmar Islands dying?).
Fontan crushed OR. Fontan was destroyed by Perdan+Caligus+Westmoor after being shrunk by Sirion.