Like his grandfather, Hezekiah, Josiah reforms Judah. He is spared from national defeat, but his sons are not. They rebel against God and pay the price by being defeated by Egypt. Egypt is using Judah as a buffer against Babylon, which is the rising power of the day. The rest of Judah’s kings are evil and suffer defeat at the hands of the Babylonians until Judah is completely destroyed. God’s promise to Hezekiah is fulfilled.
Despite God’s patience, generations of disobedience eventually lead to defeat. Even in defeat though, God continues to work as we will see later in books like Daniel.