Chapter twenty-one shows us that Ahab took Naboth's vineyard by force in injustice.
Naboth had a vineyard close to Ahab's residence. Coveting this vineyard, Ahab told Naboth to give it to him that he might have it for a vegetable garden. Naboth, not afraid of the king, refused to give the inheritance of his fathers to Ahab (vv. 1-4).
In verses 5 through 16 we read of Jezebel's evil plot to get rib of Naboth through the elders and nobles and to take possession of his inheritance.
Jehovah sent Elijah to condemn Ahab, saying that because of the evil he did to Naboth, in the place where the dogs licked up the blood of Naboth, the dogs would lick up Ahab's blood also (vv. 17-19). Elijah went on to tell Ahab that all his posterity would be cut off and that the dogs and birds would eat them because Ahab had sold himself to do what was evil in the sight of Jehovah through Jezebel's inciting (vv. 20-26).
Ahab repented and humbled himself before God. Because of this, God said that He would not bring the evil upon him in his days but would bring the evil upon his house in his son's days (vv. 27-29). Here we see that to some extent God was merciful even to such a man as Ahab.