From what he understood from Kael, there had been a big fight between the humans. A civil war, if he had to name it, which wasn't good when you consider they already had an enemy that was much stronger, that being the Demon of Dread and the Tides.
The war lasted for a long time, years on end, humanity fought, which is maybe why they had not made that much progress when it came to fighting back against the Tides.
There had been many deaths, to the point where the Tides were almost overloaded with souls, which is how many of the ruins got created inside the Tides, but with so many people inside the Tides, most went insane.
...
And this was something he had just now found out about this world... that insanity turned you into a monster, it was how the monster repopulated.
So the Tides went from being infested by humans to being a place dominated by monsters who used to be humans that had just gone insane from the place.
