Which northern city, "formerly the head of all these kingdoms," did Joshua capture and burn?

Answer: Hazor

Joshua captured Hazor and put its king to the sword, because Hazor had been the head of all those kingdoms; then he burned it.

“At that time Joshua turned back and captured Hazor and put its king to the sword, because Hazor was formerly the head of all these kingdoms. The Israelites put everyone in Hazor to the sword, devoting them to destruction. Nothing that breathed remained, and Joshua burned down Hazor itself.”— Joshua 11:10-11 (BSB)