Jamieson, Fausset and Brown on 2 Kings 18:7-8

7-8. he rebelled against the king of Assyria--that is, the yearly tribute his father had stipulated to pay, he, with imprudent haste, withdrew. Pursuing the policy of a truly theocratic sovereign, he was, through the divine blessing which rested on his government, raised to a position of great public and national strength. Shalmaneser had withdrawn from Palestine, being engaged perhaps in a war with Tyre, or probably he was dead. Assuming, consequently, that full independent sovereignty which God had settled on the house of David, he both shook off the Assyrian yoke, and, by an energetic movement against the Philistines, recovered from that people the territory which they had taken from his father Ahaz (2Ch 28:18).