Then the Israelites made a vow to the Lord: “If you will let us conquer these people, we will unconditionally dedicate them and their cities to you and will destroy them.”
This was after the Lord had defeated King Sihon of the Amorites, who ruled in the town of Heshbon, and King Og of Bashan, who ruled in the towns of Ashtaroth and Edrei.
“After we had passed through Moab, the Lord told us, ‘Now, start out and cross the Arnon River. I am placing in your power Sihon, the Amorite king of Heshbon, along with his land. Attack him, and begin occupying his land.
But the Lord said to me, ‘Don't be afraid of him. I am going to give him, his men, and all his territory to you. Do the same thing to him that you did to Sihon the Amorite king who ruled in Heshbon.’
The people of Israel took all the valuables and livestock from these cities and kept them for themselves. But they put every person to death; no one was left alive.