Judges 11:4,5 - Joseph Benson’s Commentary on the Old and New Testaments

The children of Ammon made war against Israel The Ammonites had oppressed them eighteen years, and now, when the Israelites begin to make opposition, they commence a war against them. The elders of Gilead went to fetch Jephthah By direction from God, who both qualified him for, and called him to the office of a judge, otherwise they would not have been at liberty to choose a base-born person.