[@The Omnipotent Sphere]
Well, considering they will probably know about any incoming attacks because of the spies they'd probably already have multiple traps and ambushes set up on the border. Also, if a large enough army were to attack that it threatens the nation that bad, they'd Rusia-in-WW2 it. Destroying the enemies' food and supplies and destroying any villages they would pillage on the way to any main cities (or maybe just Cupiditas if the situation is that dire) so that by the time an army reaches the walls of Cupiditas or an important city, they are so weak that they cannot stage a proper siege. Also remember that these guys are masters at ambushing. Don't underestimate this style of warfare.