The word Amorite
is used in its narrow sense here to refer to the inhabitants of the central mountain region of Palestine. Technically, only Jerusalem and Hebron were in the hill country, but the designation of the entire army as Amorite probably shows the importance of Jerusalem, with its king at the head of the coalition.1
5 Then the five kings of the Amorites, the king of Jerusalem, the king of Hebron, the king of Jarmuth, the king of Lachish, and the king of Eglon, gathered their forces and went up with all their armies and encamped against Gibeon and made war against it.