What does 1 Kings 2:32 mean?

'The Lord will pay Joab back for the murders he committed—killing two innocent men, Abner son of Ner and Amasa son of Jether, commanders of Israel's army. He killed them in peacetime as if it were war, staining himself and my father's family with their blood.' 1 Kings 2:32 - Modern Text Bible

(Solomon explains that Joab's violent actions are the reason for his execution, fulfilling justice for past wrongs.)