Albert Barnes Commentary 1 Kings 4:21

"And Solomon ruled over all the kingdoms from the River unto the land of the Philistines, and unto the border of Egypt: they brought tribute, and served Solomon all the days of his life." — 1 Kings 4:21 (ASV)

Solomon’s empire, like all the great empires of Asia until the time of the Persians, consisted of a collection of small kingdoms, all ruled by their own kings (1 Kings 4:24). These kings acknowledged the suzerainty of the Jewish monarch and paid him “presents”—that is, an annual tribute (see 1 Kings 10:25).

Unto the land of the Philistines—There is no word corresponding to “unto” in the Hebrew. The construction should be, “Solomon reigned over all the kingdoms from the river (that is, the Euphrates), over the land of the Philistines,” and so on. The writer draws attention to the fact that the extent of Solomon’s kingdom was in accordance with the promises made to Abraham, Moses, and Joshua.