To say that this story is underrated would be doing it a disservice.
A really amazing plot and while it’s not that original with the whole humans enslaving the rest of the races, it is how the details are carried.
It is a well crafted world, where everything is balanced, it’s a fresh premise in that a failed king gets a second chance, as in he succeeds in creating the non human city but only to fail and he gets to redo it.
It’s like reading slime isekai somewhat.
I highly recommend reading this manhwa, one of the few that has great combat and art with a really decent story.