The Brotherhood of Steel (BoS) is a techno-religious organization operating across the ruins of post-war North America, with its roots stemming from the American military and the government-sponsored scientific community from before the Great War.
Roughly 15 years ago, the members of the Brotherhood began disputing amongst themselves over the need for new recruits versus their secrecy as an organization. The elders ruled against sharing the technology with outsiders, convinced that they would endure what they had before. Further discussion was discouraged when the elders ordered the minority who wished to share their technology on a mission across the wastes. The Brotherhood constructed airships and dispatched the minority East, to track down and assess the extent of the remaining super mutant threat. However, as they traveled over the Big Empty a great storm broke the airships and flung them far and wide.
One ship crashed near the ruins of Champaign, Illinois. The only survivors were three initiates and one Scribe. These four continued tracking one of the groups of Super Mutants, but didn’t have the manpower or firepower to assault them directly. Along the route, the four picked up new people, each one a survivor of the Super Mutants coming through.
The Super Mutants eventually stopped when they came to Ryder-Patton. The Brotherhood survivors and new recruits, now identifying themselves as the Steel Legion, set up a stronghold to the west. They still don’t have enough manpower or firepower to take down the remaining mutants, so they wait, gathering information, equipment, and new talented recruits.