Tribal warfare is often ritualized [1]. I remember reading that the tribes on what is now Canada's West Coast practiced real, brutal warfare compared to their eastern counterparts, due to the scarce resources.
In Burden of Dreams [2], the documentary about the making-of Werner Herzog's Fitzcarraldo, some of the tribal extras would occasionally go off in their motor boats for raids on neighbouring tribes. It's so interesting to me, tribal life would be fascinating to experience.