From Arnon even unto Jabbok ... - The land bounded by the Arnon on the south, by the Jabbok on the north, by the Jordan on the west, and by the wilderness on the east was, of old, the kingdom of Sihon, but then the territory of Reuben and Gad.
Related Commentaries of Judges 11:13
Judges 11:13
13 And the king of the children of Ammon answered unto the messengers of Jephthah, Because Israel took away my land, when they came up out of Egypt, from Arnon even unto Jabbok, and unto Jordan: now therefore restore those lands again peaceably.