I think we shouldn't get confused between motivation for leaders vs. followers in this.

Followers might fight for any number of reasons. But they need leadership, armament, some sort of training, logistical support, and community support in order to sustain any kind of struggle. War being "fun", or seen as honorable, or a crucible of manhood, or any of the other stuff that gets sold in USMC commercials is not really a sustaining motivation IMO, and not one that makes a middle-aged retired officer, probably with a family to support, risk his life and that family day in and day out.