Amaziah becomes king and immediately kills his father's killers, but not their kids, because that would be wrong. Then he raises an army of 300 000 and hires 100 000 more mercenaries, but one of his prophets comes up to him and begs him not to take the Israelites, because god doesn't want like them. So he sends them home, but they're mighty pissy about it. Then he kills 10 000 children of Seir outright and throws another 10 000 off a cliff. Why, we don't know, but they're definitely all guilty of... something.
Meanwhile the soldiers he sent back kill and pillage 3000 people in Judah.
Back to Amaziah, who has started to worship the gods of Seir. His prophets try to warn him, but in the end he refuses to repent and kindles god's wrath. He sends word to Joash that he wants to meet with him, but Joash uses a parable about thistles, cedars and wild boars that translates to: fuck off. But they fight nonetheless and Judah is roundly defeated. Joash breaks down the walls of Jerusalem and pillages the city. Amaziah flees, but is killed anyway.
Uzziah is Amaziah's 16 year old son. At first, he's great: he rebuilds the walls of Jerusalem, defeats the Philistines, and invents a cunning automatic-arrow launcher/catapult that would totally land him on the Discovery Channel if he hadn't likely borrowed it from the Romans, who are definitely not credited here.
But like all the kings in Kings, he gets too big for his breeches and does something wrong. In this case, he burns incense even though he isn't a priest. The real priests try to warn him, but he ignores them so god gives him leprosy. Beware, all you incense-burning laymen!
The boring story of Jotham, a good king who rebuilds the temple, helps old ladies across the street and gives candy to children.
Ahaz is everything his father wasn't: false idols, child sacrifice, burning incense! So god sends the Syrians and the Israelites to defeat him and kidnap his people. One of them kills 120 000 of his people, another kills his son and closest slaves. Then they carry off 200 000 women and children. A priest warns the Syrians not to sin, so they take the captives back to Jericho.
Meanwhile, Judah is being invaded on all sides because of Ahaz' shenanigans. He asks the king of Syria for help, but doesn't get it, because he's so bad, he's started worshipping the Syrian gods as well. Then he dies and isn't buried with his ancestors. The shame!