Joshua 11:7

‘ So Joshua came, and all the people of war with him, against them by the waters of Merom, suddenly, and fell on them.'

The huge army gathered together, were probably still arranging tactics and leadership, not realising how close the Israelites were, when without warning the Israelite men of war, whom their scouts had probably told them were safely well out of the way, suddenly emerged and swept down on them catching them totally unawares. Their horses and chariots were unready and they panicked. They knew the fearsome reputation of these barbarians, and that they were seemingly invincible, with a God Who could do wonderful things. The alliance was a hotchpotch of armies, without unity, and may well have begun to fight each other, for in the panic they would be strangers to each other. Whatever the situation their unpreparedness resulted in panic and flight.