Uh... we were just attacking a realm closest to us and it just happened to be Westmoor. After all, this game is designed to attack your neighbours and the only non-Sirionite ally happened to be Westmoor.
With a new king, maybe we can change that
Who knows. Also, once this war ends, Zakilevo will be retiring so that could change things as well. Maybe the next prime minister won't be as aggressive as Zakilevo.