The most numerous kind of demon are no doubt the hirth'an, these form the bulk of underworld population, bringing life to the various cities of the underworld, from the greatest metropolis to the minor towns.
These demons are the ones forming ranks in the armies of most greater demons, fighting to their last breath in times of war. In times of peace they stay in their cities, living a life similar to a mortal's one, with the risk of a bigger demon looking for a prey, but that is part of the militia's job.
Due to the treacherous nature of demons and they eternal need to raise their position in their society various aristocrats will raise revels to put themselves in positions of power, but by the same logic others fund militias to keep order in the place and themselves in power. The greater demons treat this more as a petty infighting and wont intervene unless another greater demon is taking part in the rebellion to seize the territory for himself.
Those who join these militias and revels hope to get improve positions if they help maintain or change the system, being willing to risk their lives for it.