The Brotherhood-Vipers conflict was a conflict between the Brotherhood of Steel and the Vipers that lasted for a month in 2155.
In the early 2150s, a raider group known as the Vipers began to rise to power in the badlands to the south of the Lost Hills Bunker. Driven by a religious frenzy as well as the need to provide for their much larger numbers of soldiers and disciples, they began raiding more frequently. Eventually, they attracted the attention of the Brotherhood of Steel.
In 2155, the Brotherhood sent out a few scouts to track the Vipers down. This was more of a training exercise conducted by the High Elder than anything else, as the Brotherhood was convinced that a small detachment of troops in Power Armor would be sufficient to deal with a group of raiders, no matter how large. One Brotherhood squad, led by High Elder Maxson, encountered the Vipers. Expecting the raiders to break and run at the sight of soldiers in Power Armor, Maxson did not take into account the religious zeal and ferocity of the Vipers, or their poisoned weapons. A single arrow cut him while his helmet was off, causing him to die a few short hours later. John Maxson, his son, took up the role of High Elder, and Rhombus became the new head of the Paladins and the order of Knights.
The Paladins, now led by Rhombus, began a full scale campaign against the Vipers, tracking them down and wiping out almost all of their members within the span of a month.
Some of the Vipers were able to flee east into the Sierra Nevada mountain range and beyond, but they would never be as strong as they were before.
During the campaign, the Brotherhood sent a few scouts and emissaries to the Hub to track down the Vipers' members, and from these beginnings, the Hub and the Brotherhood opened full trade relations. Caravans had delivered to the Brotherhood before, but not long after the destruction of the Vipers, caravan trains ran directly from the Hub to the Brotherhood's headquarters at Lost Hills on a regular basis.