John Wesley on 1 Chronicles 5:9

Euphrates - From Jordan and the wilderness beyond it unto Euphrates. Or, of the wilderness, which lies towards or reacheth to the river Euphrates, namely, the great wilderness of Kedemoth, Deut 2:26, which was extended far and wide towards Euphrates: for that was the eastern border of Reuben's possession, and not Euphrates, to which their habitation never reached. Multiplied - Which forced them to enlarge their habitation as far as they could towards Euphrates.