If the Golden Khanate were to attack Great Zhou from the Northwest, the first ones they would actually have to face are not Su Xin, but Big Snow Mountain and those alien races from the Northwest.
Therefore, Su Xin is not worried about this region in the Northwest, what Great Zhou truly should be concerned about is the Central Plains hinterland.
The border between Beiyuan Province and the North Border is too long. If the strength of the Golden Khanate equals that of Great Zhou, the border would definitely be indefensible for Great Zhou.
However, these matters are not for Su Xin to worry about, as naturally, the Military will address them.