Albert Barnes Commentary Judges 6:4

"and they encamped against them, and destroyed the increase of the earth, till thou come unto Gaza, and left no sustenance in Israel, neither sheep, nor ox, nor ass." — Judges 6:4 (ASV)

Gaza indicates the extreme southern point to which they spread their devastations, crossing the Jordan near Bethshan (Scythopolis), entering by the valley of Jezreel, and sweeping along the whole of the maritime plain or Shephelah.