The cause can be anything you wish, but you should represent it as progressive: it fits the times, it is on the side of the future, so it is destined to succeed. If necessary, you can give it a veneer of spirituality. It is best to have some kind of enemy to hate—an enemy can help a group to define itself in opposition. Ignore this step and you are left with an army of mercenaries. You will deserve the fate that usually awaits such armies.
