It is expected that now he will begin to wage war against the Ammonites. For that is the reason he was chosen to lead the Gileadites. But what happens instead is a long negotiation with the king of the Ammonites, initiated by Jephthah, recorded in Judges 11:12–28. The report of the negotiations is unexpected, as this is the only instance in Judges whenre this method is used in an attempt to settle a dispute.
12 Then Jephthah sent messengers to the king of the Ammonites and said, “What do you have against me, that you have come to me to fight against my land?”