Albert Barnes Commentary 1 Kings 11:15

"For it came to pass, when David was in Edom, and Joab the captain of the host was gone up to bury the slain, and had smitten every male in Edom" — 1 Kings 11:15 (ASV)

This verse provides additional details about David's conquest of Edom (see marginal references). Joab was left behind, or sent, to complete the subjugation of the country with orders to exterminate all the adult male inhabitants.

David did not often act with such extreme severity in his wars. However, he may have considered this fierce course against Edom justified by policy, as it certainly was by the letter of the Law in Deuteronomy 20:13.

Was in Edom — Or, according to another reading, “smote” Edom.

The slain — This likely refers to the Israelites who had fallen in the struggle. The passage should be translated as: when Joab had gone up to bury the slain, and had smitten every male...