@Mangon, the moment the king moved his army, other country tried to invade. Whether he move his army or not the country suffer the same fate if not for the mc.
Atleast by choosing his priority, he could by time.
He can evacuate and empty the fort, but realistcally speaking, i can think of many problem that will go along with
It.
If you were in the position of the king, what other alternatives can you think of?