Charles Ellicott Commentary 2 Kings 14:22

"He built Elath, and restored it to Judah, after that the king slept with his fathers." — 2 Kings 14:22 (ASV)

He built Elath. —The pronoun is emphatic; he, in contrast with his father. “Built,” either rebuilt or fortified. The verse is in close connection with the preceding narrative.

Amaziah perhaps had not vigorously pursued the conquest of Edom, having been greatly weakened by his defeat in the struggle with Jehoash. He may even have suffered some further losses at the hands of the Edomites; and this, as Thenius supposes, may have led to the conspiracy that brought about his death and the accession of his son. The warlike youth Uzziah took the field at once and pushed his victorious arms to the southern extremity of Edom, the port of Elath (2 Kings 9:26), and thus restored the state of things that had existed under Solomon and Jehoshaphat.

After that the king slept — i.e., immediately after the murder of Amaziah. Thenius explains the verse with most success, but this clause is still somewhat surprising.