Barring something really really drastic, there is no way those two groups are gonna get along, such as sharing the *same* land. They hate each other bone deep. The hatred is pounded into them from childhood. Each is a Grand Victim, and the other side is Pure Evil in their heads.

Get an international coolition and forcefully go in and put up the biggest fattest wall the earth has ever seen. Otherwise they are gonna drag the rest of the world down to hell with them. They are already doing it.