Albert Barnes Commentary 1 Kings 4:24

"For he had dominion over all [the region] on this side the River, from Tiphsah even to Gaza, over all the kings on this side the River: and he had peace on all sides round about him." — 1 Kings 4:24 (ASV)

On this side the river - that is, the region west of the Euphrates.

Tiphsah, or Tiphsach, is the place on the Euphrates called Thapsacus. The word means “ford” or “passage,” as it is formed from the Hebrew pasach, meaning “to pass over” (compare “paschal”). It is the modern Suriyeh, forty-five miles below Balis, at the point where the Euphrates changes its course from south to southeast by east. The stream is fordable here, and nowhere else in this part of its course. Solomon’s possession of Thapsacus would have been very favorable to his schemes of land commerce (1 Kings 9:19).

To Azzah - that is, Gaza.

All the kings - Compare Joshua 12:9-24. In Philistia, small as it was, there were five kings (1 Samuel 6:18). Syria was divided into numerous small states, with as many as thirty-two kings being mentioned on one occasion (1 Kings 20:1). The Hittites were ruled by a great number of chieftains or princes (1 Kings 10:29; 2 Kings 7:6). Twelve are mentioned in the Assyrian inscriptions.