Albert Barnes Commentary 2 Kings 19:36

"So Sennacherib king of Assyria departed, and went and returned, and dwelt at Nineveh." — 2 Kings 19:36 (ASV)

Dwelt at Nineveh - The meaning is not that Sennacherib made no more expeditions at all—which would be untrue, as his annals show that he warred in Armenia, Babylonia, Susiana, and Cilicia during his later years. Rather, it means that he confined himself to his own part of Asia and no longer invaded Palestine or threatened Jerusalem.

Nineveh, marked by ruins opposite Mosul, appears here unmistakably as the Assyrian capital, which it became toward the end of the 9th century B.C. It was previously mentioned only in the book of Genesis. Sennacherib was the first king who made it his permanent residence. Its great size and large population are noted in the description of Jonah (Jonah 3:2–3; Jonah 4:11), whose visit likely occurred around 760 B.C.