Albert Barnes Commentary 2 Kings 17:8

"and walked in the statutes of the nations, whom Jehovah cast out from before the children of Israel, and of the kings of Israel, which they made." — 2 Kings 17:8 (ASV)

Idolatry was worse in the Israelites than in other nations, since it demonstrated not merely foolishness and a gross carnal spirit, but also profound ingratitude (Exodus 20:2–3).

The writer subdivides the idolatries of the Israelites into two classes: pagan and native—those they adopted from the nations they drove out, and those their own kings imposed on them. The first category includes the majority of idolatrous practices described in 2 Kings 17:9–11 and 17:17: the “high places” (2 Kings 17:9, 11); the “images” and “groves” (2 Kings 17:10); causing their children to “pass through the fire” (2 Kings 17:17); and the “worship of the host of heaven” (2 Kings 17:16). The second category includes the principal points mentioned in 2 Kings 17:12, 16, and 21.

Which they had made - The word “which” refers to “statutes.” The sentence explains that the Israelites had “walked in the statutes of the pagans, and in those of the kings of Israel, which statutes the kings themselves had made.”