From the description it sounds like it is talking about the war the Dani people in the Baliem Valley fought in that region. They did not keep written records but archaeological and anthropological evidence suggests it could have been going on for thousands of years.

Basically, two tribes were separated by a river. If someone was caught alone near the river by the other tribe they would often be killed, and there were also occasional cross border raids that might kill a couple people.

In their culture they believed this created a spiritual imbalance. To satisfy the ghosts of the people killed the two tribes would schedule a formal massive fight on the border.

They would shout insults and throw spears and shoot unfeathered arrows (they had not discovered feathered arrows). You can't really aim an unfeathered arrows and they weren't all that good at spears at that distance either so casualties were random and rare, and usually only people who didn't pay enough attention and failed to dodge.

They would usually end as soon as someone got serious injured, or if it rained or got dark. They weren't really trying to actually kill each other, they were just satisfying their obligations to the ghosts.

In the early '60s the Dutch and then Indonesia forcefully put an end to it, and Christian missionaries arrived and managed to convert the population, and the spirit-and-revenge system that required appeasing ghosts through ritual warfare went away.

That Dani are now part of the modern world, but they have an annual Baliem Valley Cultural Festival where they dress in traditional tribal clothes and recreate the ritual arrow and spear battles (safely, I presume!) to preserve their history and to attract tourists.