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. (1 Kings 4:21)
Solomon’s empire consisted, in part, of a group of small, semi-independent vassal states that were ruled by their own kings but acknowledged the suzerainty of the Hebrew king and paid him an annual tribute. The fact that Israel’s neighbors had now been destroyed or reduced to servitude is further emphasized in ch. 9:20, 21.
The river.
The Euphrates (Gen. 15:18; Joshua 1:4). The writer is drawing attention to the fact that the kingdom of Solomon had reached an extent in accord with the promises made to Abraham, Moses, and Joshua. See The Empire of David and Solomon.
All the days.
It was only during the lifetime of Solomon that this empire endured. States such as the one over which Solomon reigned, composed in part of a number of kingdoms loosely held together, often rose rapidly, and as rapidly fell to pieces.