Bible believers don't need to worry about the Geneva Convention. God tells them directly what to do with their POWs in the Bible. All they have to do is follow David's example.
David ... smote Moab, and measured them with a line, casting them down to the ground; even with two lines measured he to put to death, and with one full line to keep alive. And so the Moabites became David's servants, and brought gifts. 2 Samuel 8:1-2When it comes to POWS, we know what is right in the eyes of the Lord: kill two-thirds of them and enslave the rest.*
That is the Bible's infallible answer.
(My estimate of 667 is two thirds of the standard Biblical slaughter.)
* How do we know this is right in the eyes of the Lord? Because the Bible tells us so.
David did that which was right in the eyes of the LORD, and turned not aside from any thing that he commanded him all the days of his life, save only in the matter of Uriah the Hittite. 1 Kings 15.5God's next killing The Lord gave David victory wherever he went