The 3rd Mandalorian Crusaders were an organization which, in the Galactic Disorder era, rivaled the Galactic Jedi Republic. In most of it independent period, it was ruled by the absolute monarch, Mandalore, but in its late years, it was under the reign of Darth Admer and eventually, caused the fragmentation and reorganization of the Galactic Jedi Republic to independent systems under local governors. In the end of the Republic-Mandalorian Wars, it was united with the remains of the Sith Empire and formed the Mandalorian-Sith Empire.
Birth of the Mandalorians
The Mandalorians had a very rich heritage of ruthless and powerful empires which were issuing great anti Galactic Jedi Republic crusades which often caused the deaths of billions of citizens. This empire was created from the fragmented remains of the Mandalorian Neo Crusaders. The tale says, that the Mandalorians were a very fierce people, interested in making only their species the dominant galactic life form. After thousands of years of slow expansion and colonization until finally encountering the Galactic Jedi Republic. Battling them in numerous epic and priceless wars, they were always defeated.
Waging a last war
Even after countless defeats at the hands of the republic, the Mandalorians never gave up. They continued their campaigns for galactic domination and continued to fail, until the Sith lord Darth Admer showed up, and took command over the crusader empire and led it to victory. This empire, without another choice, joined hands with the Sith, and created the Union, which enjoyed almost two millennia of unrivaled galactic domination.