History of the IInd Legion's Foundation
The IInd Legion originally designated the Astral Wardens, and many of its founding members were amongst the ranks of the Grey Legions, while the rest of its recruits were drawn from career military families loyal to the Emperor. Tiberius Slan, who would later lead the legion, was the son of a commander in the Angkorian Dragoons, and rose through the ranks of his legion as a natural leader. From the legion's inception many of its warriors would develop potent psychic abilities, and while they could not match the raw power of the XVth Legion, their geneseed was the more stable of the two, as none of the IInd Legion developed the concerning mutations that plagued their cousins. Although the IInd Legion participated in countless theaters of war before reuniting with their Primarch, the legion's defining battle was on the world of Paramar V, a world that once served as the gateway for expansion outside Segmentum Solar. Originally sent as a forward garrison force, the IInd Legion soon found themselves fighting off an invasion force of a currently uncategorized xeno species, despite being outnumbered the IInd Legion not only survived until reinforcements arrived, but kept the planet's spaceports mostly intact for future use. It was thanks to Tiberius Slan's leadership and tactical flexibility that they won that war, so in recognition for his bravery and wisdom the Emperor himself named Slan as the legion's Lord Commander, and dubbed the IInd Legion the Astral Wardens.
By the time Lord Arwyn Clay took his rightful place leading his Legion, the Astral Wardens had accumulated a staggering number of battle honors and deeds worthy of any of his majesty's loyal warriors, and their numbers were well over five thousand strong. However, it was not until their reunion with their gene father that the Astartes of the IInd Legion achieved their full potential. The Emperor had commissioned the Mechanicum to create the Gloriana-Class Battle Barge, the Arcadia Retribution, which would not only serve as the Legion's flagship, but symbol of their unstoppable determination and power. When the time to introduce the Primarch to his legion, Lord Commander Slan personally led the 1st and 12th Companies to board the Retribution, and greet their gene sire. Like most of the Primarchs, Lord Clay enacted many changes within the legion to better suit his style of war, and while not a seamless transition, all was finished by the time the Astral Warden's final engagement called for them.
A lost kingdom of humanity, calling itself the Glormanian Confederacy, had attempted to invade the Arcadian System, with the intent of taking Arcadian clansmen as slaves, an insult the Primarch would stand for. Thankfully, the initial invasion was repelled by the combined might of the Mechanicum and a small patrol fleet from the Imperial Navy, and the would-be enslavers were denied their prize. Despite the legion mainly consisting of Terran born warriors, there was not a single Astartes who did not share their Primarch's anger, as they too felt a connection to their Lord's homeworld, and it was now in the domain of the Imperium, such transgressions would not be left unpunished. Even worse, after a careful examination of the data stored aboard the crippled invasion crafts, it was discovered that the Glormanian's had dealings with the most degenerative breed of the aliens known as the Eldar, the Drukhari. In response to the brazen attack, the Primarch answered with a plan none could have seen coming, and offered not only his Astartes, but the entire Imperium the kind of warrior Arwyn Clay truly was. Using various means, the Arcadia Retribution stole a massive asteroid nearby the Confederacy's homeworld, and used it to destroy their largest orbital defense platform. This not only drastically reduced the time it would have taken to begin a planetary invasion, but spared the resources that would have been expended to secure orbital superiority.
After a mere two weeks, the Confederacy was completely destroyed, their various human slaves liberated and brought into the Imperial fold, and the stain that was the Confederacy's social elite were erased from existence. While many might believe the speed of this victory too slow for one of the Legiones Astartes, one must remember that the Glormanian's had learned the Drukhari's blasphemous flesh sculpting, creating nightmarish abominations that filled their armies, and that they had been in power for nearly five centuries. It was thanks to Arwyn's unpredictable tactical mind that victory was secured so quickly, while also prioritizing the rescue of human slaves and prisoners from the Confederacy's vial clutches. In honor of their rightful leader's brilliance, Tiberius Slan, now the legion's Paragon Commander, held a private vote amongst the officers present for the Glormanian conquest, and unanimously agreed to not only rename the Legion, but adopt their Primarch's colors. Touched by his son's loyalty, he rechristened the legion as the Cu Sith, or Bale Hounds, in honor of a unique species on Arcadia, which according to legend were the planet's first protectors, and fiercely protective of humans.