Albert Barnes Commentary Joshua 11:7

"So Joshua came, and all the people of war with him, against them by the waters of Merom suddenly, and fell upon them." — Joshua 11:7 (ASV)

Suddenly - As before, at Gibeon (Joshua 10:9), so now Joshua anticipates his enemies. Taken by surprise, and hemmed in between the mountains and the lake, the chariots and horses would have no time to deploy and no room to act effectively; and thus, in all probability, the unwieldy host of the Canaanites fell at once into hopeless confusion.