The best way to understand about war chants is, firstly, to imagine what it would be like to be a warrior in some prehistoric tribe that is about to go to war. Imagine possible scenarios in your future - the beginning of the war, where you and your fellow warriors carefully but deliberately proceed towards the enemy (who might be a neighbouring tribe who don't yet realise they are the enemy), the actual fighting, where you are in a constant state of "kill or be killed", and, finally, the world as it will be after the war has finished. If victorious, you will have greater status in your tribe, more possessions, more territory, possibly more women. Even if your tribe does win the war, probably some of your colleagues will have died, and it won't be the same living without them. Whatever the result, life after the war will be significantly different to life before the war.
Then, after thinking these thoughts, find a piece of music that strongly intensifies the emotions which arise from thinking them. This music won't be an actual prehistoric war chant, because most of us living in the modern world have musical tastes that have been shaped by exposure to modern commercially produced music. So you will be thinking about a prehistoric war scenario, while listening to twentieth or twenty first century music.
Then, I think, you will understand, albeit subjectively, what it is that war chants are about.