Joshua 11:10

‘ And Joshua at that time turned back and took Hazor, and smote its king with the sword, for Hazor previously was the head of all those kingdoms.'

It is noteworthy that the king of Hazor, as with his successor in Judges 4, did not go out to battle himself. He had sent another, a general, to act on his behalf, probably Jobab, otherwise he would not have been there. This would be the only city that Joshua would burn with fire. That was because it was the head of the confederacy, a huge city, and therefore a constant future danger to Israel. While he could not yet occupy all these cities, he could weaken their power base.