I concur with Gabanus, First Oligarch was at war with Nivemus, Sirion and Shadowdale at first. Looking at the odds, Eponllyn decided to join the war to get more lands.
Eponllyn only has one city and 2 other regions, such a far cry from what it was back then. It is really just a simple matter of survival and opportunity, even more so due to Perdan's aggressiveness and (hatred*?) towards Eponllyn.
Hic Sunt Leones,
