David, missing Jonathan, decides to find out if any of his family members are still knocking around. Why yes, Jonathan's son with the lame feet didn't participate in the war. David sends for the boy, Mephibosheth, who falls on his face at David's feet. David promises he'll show him kindness, restore Saul's land, and they'll eat all their meals together. The reward for the old slave who told him where Mephibosheth was? He gets to till the land! And then harvest it! And cook for the bastard! Oddly, the slave, Ziba, also has 20 slaves and 15 sons.
Despite all the soaring rhetoric of 'love thy brother' and 'don't punish the child for the sins of its parents' in this book, it doesn't often come into practice. The old king of Ammon dies. You'll remember him for how he threatened to, and possibly did, gouge out the eyes of the Israelite messengers in 1 Samuel. So David decides to pay tribute to the father in the same fashion.
He sends envoys to the king, whose advisors are skeptical. So before they can carry out their plans, the king shaves half their beards and cuts half their clothing off and deports them. Well, hell, here we are 2000-odd years later and relations between Israel and its neighbours are no better.
David hears about what happened and rather than advising them to shave their beards off and start over, he tells them to hang out in Jericho until they grow back in. It must have been like the 1970s. Gross.
The Ammonites, sensing their little prank didn't go over very well, hire some Syrian mercenaries to defend themselves against David. David likewise raises an army. Apparently, mutually-assured destruction was not a deterrent back then, so they fight. And fighty-fight fight some more, until David gets into it and kills 40 000 men and 700 charioteers, and the Syrians are convinced not to fight for money anymore.