He struck its king with the sword

"Joshua killed the king of Hazor with his sword"

Hazor had been head of all these kingdoms

Hazor being the most important city is spoken of as Hazor being the head of the other kingdoms. Alternate translation: Hazor had been the most important of all these kingdoms" (See: rc://en/ta/man/translate/figs-metaphor and rc://en/ta/man/translate/translate-names)