You obviously don't know anything about the history between Coria and Eston. Coria stuck its neck out to support Eston in the past, more than the Northern Alliance has in this war.
Also, I'm curious as you didn't name any of Coria's rulers as having reason for your completely screwing over Corian/Hammarsett relations.
Like, I can understand why you are fighting CE, because most of your neighbors hate them, but why you chose to betray your Corian friend who helped found your realm I don't understand at all. Without us, you were nothing. Now we have to destroy your realm because of your actions.
Laszlo doesn't know much of anything, nor has he ever gone out of his way to rectify that (nor will he in all likelihood). That's how he can manage to be so sincerely prejudiced.
As for why we turned on Coria, you'd actually need to ask Regulus about that; by the time Laszlo took the throne we'd already fought round one and relations between our realms were fairly sour. Laszlo simply continued the previous regime's policy of political hostility, which isn't to say that he wasn't sincere about it; he very much was. But it was less personal than it was based on his overarching desire to see the Cagilan Empire lose some of its influence, and whatever your opinion on the matter is, Laszlo did and still sincerely does believe that Coria is little more than an unrepentant stooge of the Empire. Thus he never had anything personal against Saeculo, though don't doubt for a minute that Laszlo didn't like him.
In any case, I can hardly blame Saeculo for the poor relations between our realms during Laszlo's reign; Laszlo was far too biased. Saeculo would have had to do and say any number of things that he was probably both politically and constitutionally incapable of doing and saying in order to actually make a good impression on Laszlo. I just don't think that was going to happen.