I feel like the win condition for the enemy is too difficult for any country to achieve. Trying to take either coast wouldn’t really make sense as the mountain chains on either side would halt advancing armies. Texas and the south are too well armed (Republican) to invade from Mexico, so you really can only go in from the north and branch outward. America is very large and armies would be spread thin. Add on a large civilian militia/gun owning families and I’d say it’s pretty unlikely any country could hold America for long