I've been trying to delve deeper into IW lore, something only possible by adding a LOT of headcanons. But I've reached a conclusion in the middle of this. What if Aberion realized conquering everything wouldn't get him anywhere? What if he realized that the losses were too great to keep recklessly throwing his armies (and himself) into danger?
This would be the kind of occasion where he would start thinking that alliances would be much more profitable and a lot safer for his people. I consider Aberion someone with a noble purpose and someone who respects other people's. I also consider Aberion someone who would highly disapprove the cult of Verore (demon magics and stuff). These two factors make him a perfect ally for the Descendants, making up for what they lack in offense, bringing a much more effective way to fight the demons.
It's already canon that Genesis and Flame Dawn have an alliance to explore the Old World (world of the Warpath if I'm not mistaken) but how about we take it a step further? The Genesis would greatly benefit the Flame Dawn due to their far more superior technology and enhancement techniques, something the Flame Dawn could benefit even more due to their natural physical strength, which is higher than most Genesis sodiers when not enhanced.
From these arguments it is now a headcanon of mine that these three factions formed the Infinity Alliance to fight against the Verore and, on occasion, the Sleepers or anything else the alternate universes can throw at them.