If you remember back in Deuteronomy, God killed everyone in the "land of the giants." Here he helps Joshua do it again.
The victims were the Anakim, who are described elsewhere in the Bible (Deuteronomy 1.28, 2.10, 2.21, and 9.2) as "a people great and tall" -- which is biblespeak for "giants".
Joshua ... cut off the Anakims from the mountains, from Hebron, from Debir, from Anab, and from all the mountains of Judah, and from all the mountains of Israel: Joshua destroyed them utterly with their cities. There was none of the Anakims left in the land of the children of Israel. Joshua 11.21-22Since Joshua utterly destroyed all their cities and no Anakim were left alive, I estimated the number of victims to be 5000.
God's next killing: The Lord delivered the Canaanites and the Perizzites