So basically, the outer gods created orcs to scout out new territories, humans killed the outer gods and thus the ones keeping the orcs in line, and their orcs went rampant when there wasn't a outer god to propagate their species thus the whole raiding human territory for wives thing (aka orcs are vikings i guess?)
@RamenRider
I'm not sure that is what the story is going for, besides considering karna is stronger than literally everyone on the planet and the tone of the story he'll probably figure out a way to fix this is my guess.
@GrayBypasser
As i said in my first part, more than likely it wouldn't have turned out as bad if the outer gods hadn't been killed, orcs were essentially created as the same way as we'd make robots or other types of machines for exploration, when the outer gods died (or if humanity went extinct but their androids were still functional), both their reason for existence as well as their way to propagate normally was gone, so the race essentially went mad.
It's not like it's a defensible stance, but you can't really blame the outer gods for something they had no chance to fix (the outer gods are essentially implied to be like the greek gods, aka falliable).