Charles Ellicott Commentary Judges 11:13

"And the king of the children of Ammon answered unto the messengers of Jephthah, Because Israel took away my land, when he came up out of Egypt, from the Arnon even unto the Jabbok, and unto the Jordan: now therefore restore those [lands] again peaceably." — Judges 11:13 (ASV)

Because Israel took away my land. —This was a very plausible plea, but it was not in accordance with facts. The Israelites had been distinctly forbidden to war against the Moabites and Ammonites (Deuteronomy 2:9; Deuteronomy 2:19). But when Sihon, king of the Amorites, had refused them permission to pass peaceably through his land and had even come out to battle against them, they defeated him and seized his territory.

It was quite true that a large district in this territory had originally belonged to Moab and Ammon and had been wrested from them by Sihon (Numbers 21:21–30; Joshua 12:2; Joshua 12:5). But this was a question with which the Israelites had nothing to do, and it was absurd to expect that they would shed their blood to win settlements for the sole purpose of restoring them to nations that regarded them with the deadliest enmity.

From Arnon even to Jabbok. —This refers to the space occupied by Gad and Reuben. The Arnon (“noisy”) is now the Wady Modjeb. It was the southern boundary of Reuben, and its deep, rocky ravine separated that tribe from Moab. The Jabbok (“pouring out”) was originally the border of the children of Ammon (Deuteronomy 3:16; Numbers 21:24). It is nearly midway between the Dead Sea and the Sea of Galilee and is now called the Wady Zurka.