Go to each Western nation, find a map, and you will see a different border for the Disputed Territories. The former states of Nevada, Idaho, Montana, and Wyoming splintered with the nation, leaving flinders of government scattered across their lands.
Utah claims the whole of the State of Idaho up to the Canadian border, and a large section of western Montana; the locals largely disagree, and no serious attempt to enforce this claim above southern Idaho has succeeded, although Utah colonists press on into Idaho territory.
The Lakota Territory carved itself out of sections of the Dakotas and eastern Montana, and no one really wants the area enough to dispute their claim.
The bulk of Nevada is desert, not even worth the effort of laying claim to. Most of the inhabitants southeast of the Sierra Nevadas are desert air pirates, scrub ranchers, and rattlesnakes. The Nevada mountain towns seem willing to claim allegiance to either Hollywood or Pacifica, whichever can keep the desert pirates off.
Montana and Wyoming have largely fragmented. All government is local, and the locals seem determined to keep it that way. The population is completely disgusted with national government, and aims to show that local government can perform far better than any distant bureaucracy. Portions of Wyoming and Montana have been claimed by other states, but by and large this is the most lawless and best armed stretch of the West.