Chapter 20

When this happens, a "worthless" man, another Benjamite, blows his horn and incites a revolt of the 10 tribes against David.  Israel indeed does withdraw from David.  So despite coming back to Jerusalem, the kingdom is divided to some extent.  This division didn't start with Jeroboam and Rehoboam.  In fact, it first started when David took over from Saul and Abner set up Saul's son as King.

So David tells Amasa, his new commander, to gather all the men of Israel to him in three days.  Amasa goes out, but he does not come back inside the three days.  David apparently suspects that Amasa has joined Bichri, the worthless guy, and that Israel is plotting against David and Judah, and Amasa - who fought with them as their commander with Absalom - thinks the 10 tribes might be his best bet.

David sends out men to get rid of Sheba son of Bichri, because he is seen as a greater danger than Absalom was.  Joab is in charge of the group that goes.  When they get to a certain town, Amasa comes out to greet them.  Joab "accidentally" drops his sword as he goes forward to greet Amasa.  He picks it up and continues.  He grabs Amasa by the beard, and opens his gut so that Amasa's entrails spill on the ground.  The Bible says Joab did not strike him again, and Amasa died.  Joab murders him, in a very deceitful way, then stands and watches as Amasa dies with his guts in his own hands. 

Joab is a very bad man.

Joab catches up with Sheba in an ancient town.  Joab besieges the city.  The people inside learn that it is Sheba that Joab is after, so they throw Sheba's head over the wall.  Joab goes home.