A. Josiah begins his reforms, c.629/8 BC.
Josiah was merely a child of eight when, in 640 BC, his father was murdered by government officials in the palace garden. He inherited a nation from two of the most idolatrous monarchs in the history of the nation, his father Amon and grandfather Manasseh. The record of the early days of his reign in the Bible is brief but it very quickly reports that "he did what was right in the eyes of Yahweh and walked in all the ways of his father David, not turning to the right or to the left" (2 Ki 22:1). Then, "in the eighteenth year of his reign" he began a programme of reforms, beginning the the clearsing and repair of the temple in Jerusalem and making a series of territorial advance to regain some of the lands that his grandfather had lost, and sweeping out the idolatrous sites and practices they had encouraged. The extent of his territorial reclamation is uncertain; it clearly included Samaria, as the detailed account in 2 Ki 23:15ff shows.
All this was possible, of course, only against a background of declining power of the Assyrian empire that had held the nation a vassal for more than a century.
Of particular importance in the reforms was the discovery in 622 of a once-lost book during repairs to the temple. This "Book of the Law," when it was read to the king, shook the king for the neglect that the nation had paid to Yahweh's requirements of them, and renewed the king's effort at reform. This event is recorded in 2 Ki 22:3-23:28.