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, after he had smitten every male in Edom;

When David was in Edom, [Septuagint, en too exolothreusai Dauid, ton Edoom] - when David had laid waste Edom.

And Joab the captain of the host was gone up to bury the slain. It appears from the record (2 Samuel 8:13) that David in person gained a signal victory over the Edomites in the valley of Salt (cf. Psalms 60:6; Psalms 68:1; Psalms 118:7). Beyond the bare announcement of the fact, however, no information is given; and we should have been left in complete ignorance of every circumstance connected with that campaign, but for a few incidental details introduced into this passage. Whatever was the cause of provocation given by the Edomites-whether, as appears probable from the relation in 2 Samuel 8:1, that people had taken advantage of David's absence in northern Syria, to invade his kingdom, or from some other cause of offence-he marched against them with a great army (cf. 1 Chronicles 18:12), and, having overtaken them "in the valley of Salt" (the north of the Arabah) he took summary vengeance upon them: the slaughter was immense. It was assigned to Joab, after David's return to his capital, to carry out the victory. Accordingly he proceeded to Edom, and remained for six months in that country, pursuing a war of extermination against the adult male population. There is an obscurity about the statement of Joab's going up to bury the slain-whether as Hengstenberg, Keil ... think, it refers to the Israelites who fell in the valley of Salt, and whose bodies had lain without the rites of burial until his arrival; or, as Stanley suggests, it applies to the Edomite males, whom he interred in the rocky caverns of Petra. But the revenge was dreadful; and so great was the terror inspired by the energetic and sanguinary proceedings in Edom, that no attempt to disturb the Hebrew conquerors of their acquisitions in that country was made for a long course of time.