Albert Barnes Commentary Judges 7:21

"And they stood every man in his place round about the camp; and all the host ran; and they shouted, and put [them] to flight." — Judges 7:21 (ASV)

The effect on the Midianites would be that they were surrounded by a mighty army. With their own camp in darkness, as soon as the confusion of flight began, they would mistake friends for foes, and those fleeing for pursuers. Once fighting had begun due to the first accidental mistake, the clashing of swords and the shouts of combatants within the camp, accompanied by the continuous blowing of Gideon’s trumpets outside, would make it seem as if the entire enemy force was in their camp.

Suspicion of treachery from their allies would also likely arise among the Midianites, Amalekites, and Arabs. Compare this to similar scenes noted in the marginal references.