Mountainous areas would definitely define major fault lines as highways are blown and armored vehicles consolidate land otherwise. Major rivers have generally already done that with state lines but would probably increase the squiggles somewhat.
I think its also worth mentioning that existing infrastructure may bring certain cities together, given that it isn't decimated. Its especially important to note in regions which lack certain natural resources and rely on imports.
Mountainous areas would definitely define major fault lines as highways are blown and armored vehicles consolidate land otherwise. Major rivers have generally already done that with state lines but would probably increase the squiggles somewhat.
I think its also worth mentioning that existing infrastructure may bring certain cities together, given that it isn't decimated. Its especially important to note in regions which lack certain natural resources and rely on imports.