2 Chronicles 34:3-5
3 For in the eighth year of his reign, while he was yet young, he began to seek after the God of David his father: and in the twelfth year he began to purge Judah and Jerusalem from the high places, and the groves, and the carved images, and the molten images.
4 And they brake down the altars of Baalim in his presence; and the images,a that were on high above them, he cut down; and the groves, and the carved images, and the molten images, he brake in pieces, and made dust of them, and strowed it upon the graves of them that had sacrificed unto them.
5 And he burnt the bones of the priests upon their altars, and cleansed Judah and Jerusalem.
If Josiah demolished idolatry, then why does it say Manasseh did it earlier?
PROBLEM: Here we are informed that Josiah destroyed the altars and idols, but earlier (in 2 Chronicles 33:15) Manasseh had destroyed them.
SOLUTION: No human king can root out the depraved human desire for idolatry. Therefore, Josiah had to redo the same work that his predecessor had done. A good human king can destroy idols, but not the love of idols. And, as long as this love exists, idolatry will live to rear its ugly head again and again.