Because they were rivers, so immediately you know it was a water source. Plus, these rivers flooded, which was beneficial for having fertile soil. The fertile soil meant crops could be planted there.
The idea of reincarnating and coming back into the realm of the living.
From a Darwinian perspective it could be argued that nature and war are connected since those who are the "fittest" are able to gain the most resources and survive. Therefore, one group will always be trying to take from another.
