Moreover thou knowest also what Joab the son of Zeruiah did to me, and what he did to the two captains of the hosts of Israel, unto Abner the son of Ner, and unto Amasa the son of Jether, whom he slew, and shed the blood of war in peace, and put the blood of war upon his girdle that was about his loins, and in his shoes that were on his feet. Thou knowest also what Joab ... did. The insolent and imperious conduct of that general had not only been deeply offensive to the feelings (2 Samuel 18:5-15; 2 Samuel 19:5-7), but calculated to bring reproach on the character, to injure the prospects, and endanger the throne, of David. Passing over the injuries committed directly against himself, David dwelt with strong feelings on the base assassination of Abner and Amasa.
Shed the blood of war in peace ... The obvious meaning is, that in peace he acted toward them as if they had been in a state of warfare; but perhaps these graphic expressions might be designed to impress Solomon's mind more strongly with a sense of the malice, treachery, and cruelty by which those murders were characterized.