2 Kings 1:1 - Albert Barnes' Notes on the Bible

The Moabites, who had once lorded over Israel Judges 3:12-14, were reduced to subjection by David, and treated with extreme severity (marginal reference). In the time of Ahab they were dependent on the kingdom of Israel, to which it has been generally supposed that they fell at the separation of Israel from Judah. The Moabite monument (see 2 Kings 3:4), discovered in 1869, has now given reason to believe that they then recovered their independence, but were again reduced by Omri, who, with his son Ahab, is said (in round numbers) to have “oppressed” them for “forty years.” Ahab’s death was seized upon as an occasion for revolt, and Moab (perhaps owing to Ahaziah’s sickness) easily regained her independence.