Left to Right: Vanguard, Legionnaire, and Shadow Rangers

United Imperium Vanguard:
A military branch that consists of all species who wishes to fight for the Imperium while being guaranteed Imperial citizenship or Imperial patriots who wishes to fight the good fight. Founded by Consus Larone (Tiberius' forefather) after the Holy Civil War and during the Rise of the Imperium. While Augustus was trying to rebuild from the Alliance's collapse, he didn't have enough soldiers to use in defense, liberate and conquer. Fortunately, Consus managed convince many (From humans, beastfolk, orcs, etc) to side with the new noble cause, thus later forming a foreign legion. After the United Imperium was established, the newly coronated Emperor Augustus Gustave offered Consus and his soldiers to join the Imperium as honorary citizens, many accepted but Consus refused. Instead, Consus offered Augustus an idea regarding the foreign legion being part of the Imperium. He stayed with the Imperium for a time to train officers to take his place, lay the foundation for the Imperial foreign legion that later was renamed the United Imperium Vanguard. After everything was established and set in stone, Consus left the Imperium to return to his home realm of Serenitas Perpetua. Later, he and his soon to be born children built a kingdom and formed an alliance with the Imperium in the end.

As for the Vanguard, many can join from imperials to non-imperials. However the Vanguard only seeks the best of the best what the realms holds, not many make it as a Vanguard, only ending up leaving or die in the training. But those who do make it, have their lives forever changed.

The purpose of the Vanguard is to be the piercing blade of the Imperium, the first in the fight and the last out. Over the years they've been seen as the ultimate heroes of not only the Imperium, but the realms. From liberating realms from Arvae's Elven Resurgent Empire, putting down demon incursions, and saving innocent lives. The Vanguard has done all of those not for fame and glory, they done those out of duty, what they believe is right, and/or out of patriotism.

After years of service in the Vanguard, they're given rights and perks of an Imperial Citizen

United Imperium Legion:
The main force of the Imperium, the defenders of the free realms, descendants of liberators and loyalists. While the Vanguard are the piercing blade of the Imperium, the Legion is the spear and shield. Consists of citizens who joined the Legion to protect their way of life and fight side by side with the Vanguard.

Shadow Rangers:
The Special Forces of the Imperium that answers only to the commander of the rangers and the Emperor, without question or hesitation. From sabotaging behind enemy lines, assassinations, reconnaissance, and assisting the Imperial armed forces.

Not shown in the image, but part of the United Imperium Armed Forces

United Imperium Realm Defense Force- Unlike the Legion, the defense force are trained to be security and first line defenders of the realms, until Legion/Vanguard reinforcements arrive.

United Imperium Navy- As the name explains, it's the navy.

Paladin Power Armoured Troop Corps- Another special forces of the Imperium. But unlike the Shadow Rangers, the Power Armoured Corps focuses more on the loud and the direct approach. Having access to power armour technology, heavy weapons, and testing experimental weapons.

Imperial Knight Guard- The Emperor's and the Chancellor's bodyguards. Selected and trained from birth by Augustus Gustave and the knight commander of the guard. Like the Shadow Rangers, the Knight Guard only answers to the Emperor