Jehoram, king of Jerusalem, started his reign by murdering all his brothers. Then he married Athaliah, daughter of Ahab, and she taught him to worship foreign gods. It went downhill from there.
God tolerated this only because of his promise to David that his line would endure. But the prophet Elijah sent Jehoram a letter warning that God would destroy his people, corrupt his family, and afflict him with a disease of the bowels so terrible he would watch his own insides rot. Everything came true. Arabian and Philistine armies invaded, slaughtered his sons and wives, and plundered the kingdom. Only one son, Ahaziah, survived. Then the disease struck. Jehoram died miserably after eight years, and the people refused to bury him in the tombs of kings.
In the northern kingdom, King Joram was wounded besieging Ramoth-gilead and returned to Jezreel to recover, leaving his general Jehu son of Nimshi in command. Elisha sent a young disciple to Ramoth with holy oil. The disciple pulled Jehu into a private chamber, anointed him king, and declared he must destroy the house of Ahab to avenge every prophet Jezebel had murdered. When Jehu's captains heard, they threw their garments under his feet and proclaimed him king.
Jehu rode for Jezreel. King Joram came out to meet him in Naboth's field, the vineyard stolen through murder. Jehu put an arrow through Joram's heart and ordered the body thrown onto Naboth's land, fulfilling Elijah's prophecy. Ahaziah of Jerusalem fled but was caught and killed.
At Jezreel, Jezebel painted her face and taunted Jehu from a tower window. Eunuchs threw her down. Horses trampled her. When men came to bury her, they found only skull, feet, and palms. Dogs had eaten the rest, exactly as Elijah prophesied. Jehu then exterminated Ahab's entire house: seventy sons beheaded, their heads piled at Jezreel's gates. He lured every priest and prophet of Baal into their temple under pretense of worship, massacred them all, and burned it to the ground.