Rashi
Jewish
1040–1105
“When they chose new gods—there was war in the cities. When the Yisroelites preferred modern Deities, then they needed to engage in battle in their cities. But, take note, now, when they volunteered, was a shield or battle ax in sight among the Yisroelites when they needed to do battle with the forty thousand field marshals the idolators flung against them? The Omnipresent overwhelmed them all with celestial warfare, and the Kishon stream swept them away. Cities. As in, "If there should be found in your midst, in one of your cities".”