Now we start to see the decline of Judah as we transition to a king who loved God, Jehoshaphat, to his son who was in it for himself. Look at what he does in his first 100 days in office. Jehoshaphat had many sons, but his eldest was Jehoram. As soon as he takes office he kills all of his brothers. They were a threat to him. Instead of rooting for his rivals he decides to root up his rivals and destroy them. He does so. He also "walked in the way of the kings of Israel." That is not a good thing.
God does not destroy him and his lineage because he had promised to David that his kingdom would last forever. As a result we have these splinter groups break out from Judah because they saw the unfaithfulness of the king and wanted to obey God in ways that would give God glory. Edom was one of them.
We also see the prophet Elijah, remember him, the one who killed the prophets of baal. He sends word from God that God will punish him and destroy his family except for one to take over the throne. The king is also promised to receive a disease of the bowels that would ultimately destroy him and cause a lot of pain and suffering. In the meantime the Philistines came and carried away all of the possessions of the land.
Once Jehoram dies they bury him but do not give him a kingly burial. I love the understatements that are used in this passage. Look at vs.20: "He departed with no one's regret." Basically, no one was sorry that he died. He was buried in the Jerusalem but not in the tombs of the kings. He was not respected as a king because he was so bad. I guess that's what happens when you try to go rogue and govern as you want to and not as God wants you to.