basically they just want to dominate everyone for their lord Emperor Scar. Think about hitler and the third reich and it has nothing on these guys. at the moment these guys are quite small and so have hooked up with these Nightside people to get equipment and be more powerful but of course will turn on them when they get strong enough
which explains the artillery piece, Civilized and peaceful people don't need to build massive demonstrations of power. I hope these guys don't get access to any advanced starship technology. Were it the case they could go from small to large problem.