The river — Euphrates: for so far David, having conquered the Syrians, extended his empire, which Solomon also maintained in that extent. And so God's promise concerning the giving the whole land, as far as Euphrates, to the Israelites, was fulfilled. And, if the Israelites had multiplied so much that the land of Canaan would not suffice them, having God's grant of all the land as far as Euphrates, they might have seized upon it whensoever occasion required. The land of the Philistines — Which is to be understood inclusively; for the Philistines were within Solomon's dominion. The border of Egypt — Unto the river Sihor, which was the border between Egypt and Canaan. And served — By tribute, or other ways, as he needed and required.
Related Commentaries of 1 Kings 4:21
1 Kings 4:21
21 And Solomon reigned over all kingdoms from the river unto the land of the Philistines, and unto the border of Egypt: they brought presents, and served Solomon all the days of his life.