The answer is: Ammonites

Judges 11:5

Jephthah's story, especially his conflict with the Ammonites, is packed with drama and reflects complex themes of leadership and redemption. Emerging in the turbulent times of the Judges, he was not just an ordinary leader; Jephthah had an unconventional past, often being labeled as “the outcast” of Gilead due to his lineage. He was the son of a harlot but showed tremendous courage and tactical brilliance in rallying his people against the Ammonites.

Now, speaking of the Ammonites—their history is a gripping listen. Originating from Ammon, the territory multiplied with tensions between them and Israel, dating back to the tumultuous days of Abraham. These enemies weren’t just any group; they had a geneological rant running deep. Think cousin rivalry taken to the extreme!

Jephthah's encounter with them was notable not only for its military importance but also for Jephthah’s unusual vow to God. This expressed both his desperation for victory and encapsulated the serious spiritual stakes at play. He promised God whatever came out of his house first upon his victorious return, creating anticipation that's as dramatic as a cliffhanger in TV shows today.

Isn’t it fascinating how these ancient stories echo powerful human experiences of conflict, unintended consequences, and the quest for identity? The conflict between Israel and the Ammonites framed the very essence of who the Israelites were going to be as a people—the promised descendants balancing faith, war, and legacy on steep hills of despair and triumph.