The empire - think of it as a much more ruthless version of the british empire. No regard for those they encounter, arrogant and expansionist. However, the rebels and communities sent here rebelled mostly because their once similar views of the empire changed.
This is revealed as what my character has vomited up, an old evil made from the pollutants of the empire soaking into all aspects and making them less but something more as well. The darkness is what blackens the empires hearts and makes them cruel, heavy handed. Those who have been subjugated after a generation soon become that which they fought against.
Present, the empire is at its zenith at home. Tolerated by other empires abd at present watching as it foes to war against rebels waiting for the moment to strike. The issue is, its not the empire but the darkness - a oily black that rots them from within. Its here the Empire during this war stumbled, a foe that took its assetts and burned its supply lines.
In short due to how far away the empire is, its hard for it to handle losses here. Let alone react.
