John Calvin Commentary Joshua 8:15

"And Joshua and all Israel made as if they were beaten before them, and fled by the way of the wilderness." — Joshua 8:15 (ASV)

And Joshua and all Israel made as if they were beaten, etc. This is another stratagem. By pretending to flee, they draw off the enemy to a distance, leaving them no retreat afterwards into the city, which was in flames before they suspected that any disaster was to be anticipated in their rear. Hence, while the king of Ai pursues the Israelites as vanquished, the part of the army that lay hidden towards Bethel had sufficient time to take the city, and make it too late for the inhabitants to realize that they were utterly undone. For after they had already been repulsed, and were everywhere slaughtered, they were overwhelmed with despair on seeing the flames of the city, and so completely surrounded that not an individual could escape.

The question asked here by some, whether it is lawful to overcome an enemy by wiles and stratagem, originates in gross ignorance. First, it is certain that wars are carried on not merely by striking blows; for those are considered the best commanders who accomplish more by skill and counsel than by mere violence; and secondly, the longer anyone has served to acquire experience, the better soldier he becomes. If war, then, is lawful, it is beyond all controversy that the usual methods of conquering may be lawfully employed, provided that there is no violation of faith once pledged, either by truce or in any other way.