Gammorin's Army

When the Master was defeated by the Vault Dweller, its army was fractured into a bunch of tiny pieces. Eventually, these pieces coalesced into two distinct off-shoots, with Gammorin's Army being one of them. Gammorin was a lot like the Master, in that he wanted to create a paradise on earth run by super mutants. His primary concern was the creation of new mutants, species, and most importantly: a cure for the infertility that drove the Master insane.

Background
When the Master's Army was defeated, it was up to those super mutants of higher stock to take charge and lead the battered Unity into the wasteland. Gammorin was one such mutant. Cunning, charismatic, and highly skilled as a warrior, Gammorin quickly rounded up the fractured groups and fled east, across the Bright Mountain. Eventually he stopped at what was previously known as Kansas City, at the border between Missouri and Kansas. Here he founded a new city, Oscella.

Oscella grew very rapidly. Super mutants from across the wasteland flocked to Gammorin, swelling the population to numbers not seen since before the fall. A new lab was constructed beneath the city, raiding parties were dispatched into the surounding country side, searching for humans and FEV. Both were found. A scientist named Johnathan Kensie, was captured and brought back to Oscella. He was dipped into a large FEV vat and emerged Erkal, the chief scientist of Gammorin's Army. Unlike most of the other wastelanders that were dipped, Erkal did not lose his intelligence. Indeed, his knowledge and understanding grew tenfold, indicating to Gammorin that he was of pure stock. The search for Vault 187 was on.

Vault 187
Erkal struggled to remember where his vault was, whether biologically or out of some latent compassion for his fellow vault dwellers. However, it did not save Vault 187 from discovery.

After a year of searching, around 2164, Vault 187 was discovered. It was determined that the Vault had faced a power shortage, and that a team of scientists were gathered to venture forth into the wasteland to recover some sort of sustainable power source. The teams did not succeed, and the vault had collapsed in on itself, fighting one another like petty savages. Disappointed, but hoping to salvage the effort, Gammorin captured those alive and brought them back to Oscella to be Dipped.

War with the Brotherhood
The Brotherhood and the Master fought endlessly over the vast expanse between their home bunker and Mariposa Military Base. Arguably, the West Coast division was primarily responsible for halting the mutant army's rampage. Without the Brotherhood, the Vault Dweller would have had to face overwhelming odds. When Gammorin learned the Brotherhood followed them across the wasteland in giant aluminum blimps, he was enraged. He viewed them as the primary reason for the Master's destruction, and vowed to exact revenge. Thus, the Gammorin-Brotherhood War had begun.