Charles Ellicott Commentary 1 Kings 21:26

"And he did very abominably in following idols, according to all that the Amorites did, whom Jehovah cast out before the children of Israel.)" — 1 Kings 21:26 (ASV)

As did the Amorites.—The reference is probably not only to the idolatry and worship of false gods, but to the nameless abominations always connected with such worship.