judges 11:13 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. - Free Bible Online

      13. the king of Ammon . . ., Because Israel took away my land--(See on De 2:19). The subject of quarrel was a claim of right advanced by the Ammonite monarch to the lands which the Israelites were occupying. Jephthah's reply was clear, decisive, and unanswerable;--first, those lands were not in the possession of the Ammonites when his countrymen got them, and that they had been acquired by right of conquest from the Amorites [Jud 11:21]; secondly, the Israelites had now, by a lapse of three hundred years of undisputed possession, established a prescriptive right to the occupation [Jud 11:22, 23]; and thirdly, having received a grant of them from the Lord, his people were entitled to maintain their right on the same principle that guided the Ammonites in receiving, from their god Chemosh, the territory they now occupied [Jud 11:24]. This diplomatic statement, so admirable for the clearness and force of its arguments, concluded with a solemn appeal to God to maintain, by the issue of events, the cause of right and justice [Jud 11:27].

JFB.