Like Rome Before It

When an empire falls, it very rarely leaves peace and harmony in it's wake.

As the Terran Empire grew and expanded and crushed the minor alien races in it's way, those with the time to do so began to arm themselves and form alliances for the coming war. The Greenskins released their previous population controls, to breed armies of warriors for the coming war. The Federation was first formed as a loose alliance, which was forged into a powerful empire in it's own right during it's first war with the Terrans. Other races either grew strong enough to withstand the heat or war...or they did not.

In the wake of the Terran armies came their bureaucrats, a see of little people always seeking to expand their own influence. As the Bureaucracy grew in size, corruption began to seep into the very bones of the Empire. As groups of people grew sickened and crushed by their masters, they began to resist. The speed and brutality with which these first few uprisings were crushed only fueled the fires, and soon after the groups of rebels which would become the Crusaders began to appear and to ally with each other. The Crusaders took on the iconography of a holy, righteous crusade to rally more aid to their cause, and the Crusader Lords would become major powers.

As the war expanded across the Empire, the Loyalists turned to more and more desperate tactics. Lesser alien races were enslaved, experimented on, and modified. Those deemed suitable were turned into cannon fodder for their armies. Modification experiments were expanded to include their own troops, and in extreme cases the soldiers would have very little of their humanity left. As the experiments continued, many troops would be changed to take the form of hideous monsters, and other terrible things.

The Empire military would become as fractured as the rest of the Empire. Many elite units would directly take up the Loyalist and Crusader banners. Many more would become what is now known as the orders of the Star Knights, who would often still maintain close ties with one faction or the other. Many more would forge their own empires in the ruins of civilization, or would openly become mercenary units.

Caught in the middle of all of this, most of the colonies of the Empire have formed their own militias to defend themselves. Largely formed using supplies of pro-Collapse equipment and troops, some forces of the Colonial Militas have also managed to secure sources of new made equipment, and become powerful regional forces.