The answer is: Ammonites

Judges 11:5

In the Book of Judges, Jephthah's story is one of overcoming soaring odds and struggling with complex narratives of kinship and conflict. When he stepped onto the scene, he was leading Israel against none other than the Ammonites, who were constant adversaries in the ancient landscape of Israel. The Ammonites, descendants of Lot according to Genesis 19:38, exemplify the historical friction between neighboring nations and their petty squabbles, showcasing how deeply rooted grievances can lead to cycles of conflict.

Jephthah is often considered a tragic hero—an outcast turned military leader. His background adds layers to his character; born to a prostitute and shunned by his half-brothers, he finds glory but also terrifying consequences. Interestingly, his name "Jephthah" means "He opens," hinting perhaps at his role as a leader tasked with new beginnings despite his tumultuous past.

One fascinating aspect of Jephthah's story involves his vow to God, a commitment packed with moral complexity as he promises to sacrifice the first thing that greets him if he achieves victory. This controversial vow leads to debate about the nature of true devotion and the ethics of promises made in desperation.

As Jephthah rallies his forces, we see echoes of David’s future confrontations with enemies as they both represent an archetype-like struggle—a fight not just for land, but identity. Studying these moments gives us a vivid tapestry of how personal struggles and national fights are intricately woven in the narrative of the Old Testament.