@Acolytus silly speedreader, didn't they say that the merfolk prince got killed by humans after trying to get peace (or something like that i don't remember)?
He feels bad because merfolk attacked humans with a good justification and as humanity protector he had to kill the invaders.
That's why he circled the merfolk city with Jormung whatever , so that humans don't fuck with them again and he also swore to not meddle with them as long as they don't genocide.
@Angibot exactly, humans were the initiators, whereas merfolk simply retaliated against humans aggression, but I do not remember whereas humans who were responsible for first attack on merfolk where ever punished?