C. F. Keil and Franz Delitzsch on 1 Chronicles 5:9

1Ch 5:9 “Eastward to the coming to the desert (i.e., till towards the desert) from the river Euphrates,” i.e., to the great Arabico-Syrian desert, which stretches from the Euphrates to the eastern frontier of Perea, or from Gilead to the Euphrates. Bela’s family had spread themselves so far abroad, “for their herds were numerous in the land of Gilead,” i.e., Perea, the whole trans-Jordanic domain of the Israelites.