Plains Commonwealth The Plains Commonwealth was one of the thirteen commonwealths of the pre - War United States . Created in the early 21st century , it was comprised of the former states of , , , and . Former Kansas . Before the war , Kansas was home to several military installations and a large Nuka - Cola factory in Newton . Some time after the conflict , 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 ghoul s 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 mutant s 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 duelled 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 by the robots . Former Missouri . Around that time , the super mutant camp in the area of St . Louis , Missouri was taken by surprise by an Eastern 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 Oklahoma . Vault - Tec Rejection Letters issued in the Washington D . C . area suggest that there are vaults in Oklahoma . Whether or not these vaults were completed by the time of the Great War remains to be seen . The name of the Red Okie Centuria suggests that Caesar ' s Legion may have a presence in , or connections to , the Oklahoma region . Later Times . By 2277 , the Brotherhood presence in the region had lessened , but there is still a group of soldiers maintaining a form of peace . Appearances . Parts of the Plains Commonwealth appear in " " , and the canceled " Van Buren " . It is mentioned in " Fallout 3 " . St . Louis ' also appears in the " Atomic Command " game in " Fallout 4 " .