as a follow-on question: I've heard of "ritualized" battles in some of the less developed parts of the world--remote pacific islands, rural africa, and the like.

Is that true? What was the purpouse of such a ritual? what kinds of casualties were there?

edit: as an aside, I'm pretty sure the WW1 "live and let live" concept would fall under your question, but I can't think of any good sources on the subject. Maybe /u/elos_ or somebody can give us a proper explanation?

An example that might fit would be the battle of the Horatii brothers versus the Curiatii brothers. Instead of all-out warfare between the Roman and the Alba Longa army, they each selected three men, Rome with Horatii and AL with Curiatii to fight for them. The survivor would collectively "win" the battle, as to minimize bloodshed. The Horatii won. Also, see Oath of the Horatii by Jacques-Louis David.

Machiavelli's The Prince talks about such practices in Italy, where maneuver would largely decide the outcome of battles between mercenaries and the winners would not kill the losers. He spoke of rules of warfare that (in his view) simply served to perpetuate the war longer. Recently, in the Ethiopia-Eritrea War, each side agreed not to bomb the other's cities.