2 Chronicles 34:7
And when he had broken down the altars and the groves, and had beaten the graven images into powder, and cut down all the idols throughout all the land of Israel, he returned to Jerusalem. And when he had broken down the altars and the groves, and had beaten the graven images into powder, and cut down all the idols throughout all the land of Israel, he returned to Jerusalem.
Josiah's reform extended throughout Israel in a thorough destruction of idols and places of idol worship. That extent meant carrying the campaign beyond Judah into the former territory of the ten tribes. The work reached from Manasseh and Ephraim and Simeon as far as Naphtali. Throughout that territory he broke down altars and sacred groves, beat carved images into powder, and cut down the idols. After completing this work throughout the land, he returned to Jerusalem.
This reform is connected with his later urgent inquiry to the Lord about the book of the law and Judah's threatened judgment. This reform is connected with the people's deep repentance and return to the Lord after the law was read.