Lacking a better explanation/model, I’ll go for this.
I’ll just add that religion, in the form of fear of the anger of the gods, and the threat of a miserable existence in the afterlife is a very powerful control mechanism. I find it reasonable to hypothesise that as soon as people in power discovered that this fear could be used to control and alter people’s behaviour, it became a thing of its own. They could therefore actively use it to keep people in line, and to use it as a common cause to promote internal cooperation. This cooperation could then be exploited to get – among other things – better internal structure to improve the survivability of the tribe, to mobilise better and stronger defense against external threats, and of course to bring riches to the tribal leaders/the men in charge of the tribe. Similar mechanisms can be seen at work also in non-religious contexts these days.