What does 2 Samuel 17:25 mean?

Absalom put Amasa in charge of the army instead of Joab. Amasa was the son of a man named Ithra, an Ishmaelite, who had married Abigail, Nahash's daughter and Joab's cousin. 2 Samuel 17:25 - Modern Text Bible

(Absalom replaces Joab with Amasa, who is related to Joab, showing shifting loyalties and family ties.)