When everyone has pounded the snot out of each other and the whole place has no more people in it.
Sorry to be pessimistic, but it seems as if the only peace that can come out of this is when there are no more people left to fight.
Grasshopper Wars come to mind:
Long, long ago, in the pine barrens of Lenapehoking, where modern day Flemington, New Jersey, now stands, there was a Lenapé village. This was before the wapsitak, the white ones, came to our shores. Across the river, in what is now Pennsylvania, another village stood. Some say it was another tribe, some say it was another village of Lenapé. Either way, the people of the villages liked to visit back and forth whenever they could. The men of the villages would hunt together, the women of the villages would work together, and the children of the villages would play together.
One day, as the children were playing together, a boy from the village across the river saw a streak of green in the grass and, following it, soon caught the largest grasshopper he had ever seen. He laughed happily as he played with his new pet and soon a group of the other children gathered around him. He showed them all the grasshopper and how agile it was. They all agreed that it was the largest grasshopper they had ever seen.
But one of the boys from the first village grew envious, and he began to scowl and fret. Why shouldn't he have that large grasshopper? After all, was it not found on his village territory? Hastily, he snatched the grasshopper from the other boy and this set off a fight. Then, like a chain reaction, a free-for-all began between the children of the two villages.
Soon all of the children were involved in the fray. The battle quickly polarized between the villages, each child siding with his village brothers and sisters. Hearing the screams of the battling children, the village women rushed from the fields and lodges where they were working. Seeing their children attacking one another, they too joined the battle and began defending their children. Soon they too were pummeling one another and pulling hair.
When the men returned from the day's hunt, they found their women and children huddled all around; injured, bleeding and worn out from the prolonged fight. None of them could recall any longer why the fight had taken place, and could only tell of being attacked by the members of the other village. Anger then grew between the men too, and they took their women and children to their respective villages. The village chiefs swore vengeance on the opposing village and the friendly exchanges between the villages ceased.
It was many seasons later that the truth was discovered. What had begun as child's play and a jealous argument grew into an unnecessary fight and long seasons of discontent between the two villages. Friendships were lost and much unfounded anger was exchanged. And this fight is remembered in our histories as "The Grasshopper War".
http://www.geocities.com/shabak_waxtju/grasshopper_war.html">from the Lenape