Let’s do a quick review of people and places:
“Amorite” is a general name for “Canaanite,” the people Israel was to drive from the land.
“Ammonite” and “Moabite” denote descendants of Abraham’s nephew, Lot.
“Edomite” denotes the descendants of Jacob’s brother, Esau.
The Ammonites, Moabites, and Edomites all lived outside the land of Canaan, east of the Jordan river.
In Judges 11, the Ammonites oppress Israel and Jephthah goes to war with them. But before doing so, he asks why they are being oppressed. The Ammonite king responds that Israel, in the Exodus story, took their land and now he wants it back. Jephthah responds in a detailed way, showing that Israel avoided conflict with her kinsmen, the Moabites, Ammonites, and Edomites and neither took nor encroached on their territory. In point of fact, Sihon, an Amorite king, had conquered the territory in question and Israel had legitimately conquered him. Thus the land belonged to Israel.
Jephthah’s argument has four parts: First, the land in dispute did not belong to Ammon. Second, Ammon had not, in three hundred years, questioned fact one. Third, Ammon’s god gave Ammon her land – she should be happy with what her god had given her and leave Israel alone with the land Israel’s God had given Israel. Fourth, Ammon should beware. Balak, the king of the Moabites knew better than to trifle with Israel. The Ammonites should take note.
But they didn’t, and the Lord gave Jephthah victory over them.
The part everyone focuses on in this story however is the part at the end about Jephthah’s daughter. I see no way to view this story except that Jephthah did what he vowed to do and sacrificed his daughter to God (note 11:39). It was a stupid vow.
And that, I think, is the point.
At the beginning of the Jephthah story, we are told how Israel fell under the influence of the evil people around her who engaged in human sacrifice. No matter how loyal Jephthah might have seemed in this chapter, not even he could avoid the influence of the Canaanites. Though God rescues them repeatedly, Israel has become like the people around her.