Why hasn't the world's dream of peace among all groups and races come true yet?

Les teaches that the world wants a utopia of peace and prosperity and peaceful living between all the various groups and races. But that peace is not going to happen until the Prince of Peace comes. The passage pictures future harmony in creation: the wolf dwells with the lamb, the leopard lies down with the kid, the calf and young lion and fattening are together, and a little child is in their midst and leads them. The cow and bear feed together, their young lie down together, and the lion eats straw like an ox, losing his carnivorous appetite and reverting to grass and forage as before sin entered. The suckling child plays on the hole of the asp, and the weaned child puts his hand on a cockatrice den; they do not hurt or destroy in all God's holy mountain, which in Scripture is a kingdom. When the earth is full of the knowledge of the LORD as water covers the sea, that is the peace the Lord's prayer instructs to pray for.