The Northern Commonwealth was one of the thirteen commonwealths of the pre-war United States of America. Created in the early 21st century, it was comprised of the former states of Montana, Wyoming, North Dakota and South Dakota.
Appearances
The Northern Commonwealth does not appear in any released Fallout games, though it is mentioned by the Courier in Fallout: New Vegas.
If the Courier convinces Papa Khan to end the Great Khan's alliance with Caesar's Legion and leave the Mojave they will travel to the remains of the Northern Commonwealth to forge a 'mighty empire'.