This verse is the customary closure of the period of reign of a king. Read this verse together with 2 Kings 14:25—together they say something about the extent of the enlargement of Israel and Judah's territory.
However, there is a problem with the part restored…to Judah.
Some commentators leave to Judah
out, for this could have been added later by mistake.
What is also a possibility is that the writer wants to highlight that Hamath and Damascus in times of the undivided kingdom fell under the reign of the royal house of Judah with King David and King Salomon. In that case we can hear some homesickness here: when we were undivided and reigned from Judah, the reign was so great that Damascus and Hamath were included in it.
28 Now the rest of the acts of Jeroboam and all that he did, and his might, how he fought, and how he restored Damascus and Hamath to Judah in Israel, are they not written in the Book of the Chronicles of the Kings of Israel?