Plains Commonwealth

The Plains Commonwealth was one of the thirteen commonwealths of the pre-War United States.

Background
Created in 1969, it was comprised of the former states of Nebraska, Kansas, Iowa, Missouri, and Oklahoma. The commonwealth bordered the Northern Commonwealth, the Four States Commonwealth, the Texas Commonwealth, the East Central Commonwealth, and the Great Midwest Commonwealth.

By 2277, the Brotherhood presence in the region had lessened, but there is still a group of soldiers maintaining a form of peace.

Former Iowa
The parents of Dr. Constance Nichols, a research scientist at the National Isolated Radio Array in Appalachia in 2076, lived in Iowa.

Former Kansas
Before the war, Kansas was home to several military installations and a large Nuka-Cola factory in Newton. Some time after the Great War, a major faction in the Kansas area was the technology-worshiping Reaver cult, based in Newton.

Some of the major towns were Kansas City, inhabited by ghouls who worshiped a nuclear bomb, the Junktown-like Junction City, Cold Water, famous for its casino and Great Bend, a major pre-War industrial center.

After the fall of the Master in the far west, a great migration of super mutants he created began. They traveled east to find themselves a new home until they found a crashed Brotherhood of Steel zeppelin, which was a part of an Air Convoy that was meant to find and destroy the remains of Master's Army. Brotherhood Paladin Latham dueled the mutant's leader, Gammorin, and won. As unlikely it may seem, Latham took his opponent's name and became the new leader of the mutant army, setting up the base known as Osceolla near the airship crash site.

Around 2197 and 2198, Kansas found itself in the middle of a war zone. Several towns, mostly pre-War centers of industry, including the inhabited Great Bend, and others like Scott City and Canyon City were taken over by Calculator's robots from Vault 0. It didn't go unnoticed by Latham/Gammorin, whose mutants started actively fighting the mechanical threat.

In the meantime, the Vault 0 robots progressed east and one humanoid robot even strayed to the area of Junction City, which, unlike most other towns of that region, still maintained independence from the Brotherhood. However, when the Reaver cult tried to take the robot parts from the city's inhabitants, they were forced to ask the Brotherhood for help. Soon, the Reavers themselves had to ask the Brotherhood for help after their main camp in Newton was taken over by the robots.

Former Missouri
As a part of the ongoing war with the Calculator, the super mutant camp in the area of St. Louis, Missouri was taken by surprise from a Midwestern Brotherhood of Steel squad. As the Brotherhood was unaware of the robot menace, they perceived the super mutants as a major threat and attacked them immediately. The mutant High Inquisitor Toccomatta took Simon Barnaky, the leader of the Brotherhood prisoner in St. Louis, and managed to escape the following Brotherhood assault that destroyed the mutant forces in that area. The Eastern Brotherhood also destroyed Gammorin's laboratory in Jefferson, Missouri, and prevented the mutants from obtaining the nuclear missile worshiped by the ghouls in Kansas City. Eventually, even the main mutant base in Osceolla was taken and Gammorin was killed, and the remaining mutants were either taken to labor camps or drafted into Brotherhood forces.

Former Nebraska
Paladin Leila Rahmani led the First Expeditionary Force across the country, from Lost Hills to Appalachia, with goals of re-establishing contact with the lost chapter of the Brotherhood. A message records the loss of contact with the group after they crossed the Rocky Mountains, with scribes estimating the unit was in the vicinity of Lincoln.

Former Oklahoma
Vault-Tec rejection letters issued in the Washington D.C. area suggest that there are vaults in Oklahoma.

The name of the Red Okie Centuria suggests that Caesar's Legion may have a presence in, or connections to, the Oklahoma region.

Appearances
The Plains Commonwealth is mentioned in Fallout 3 as well as in Fallout 76 and its One Wasteland For All update. Parts of the Plains Commonwealth appear in Fallout Tactics and the canceled Van Buren. The Gateway Arch also appears in the Atomic Command game in Fallout 4 and Fallout 76.