Albert Barnes Commentary Judges 11:33

"And he smote them from Aroer until thou come to Minnith, even twenty cities, and unto Abelcheramim, with a very great slaughter. So the children of Ammon were subdued before the children of Israel." — Judges 11:33 (ASV)

As in the conflicts with the Moabites, Canaanites, and Midianites (Judges 3); (Judges 4); (Judges 7), the battle was on Israelite territory, in self-defense, not in aggressive warfare.

The plain of the vineyards - Rather, “Abel-Ceramim” (compare Abel-Meholah), identified with an “Abel” situated among vineyards, 7 miles from Robbah. “Minnith” is “Maanith,” 4 miles from Heshbon, on the road to Rab-bah.