They also settled in the east as far as the edge of the desert that extends to the Euphrates River, because their livestock had increased in the land of Gilead.
The Reubenites spread eastward toward the desert reaching to the Euphrates because their livestock increase in Gilead. Their range grows with their herds.
This verse explains the tribe’s territorial expansion.
1These were the sons of Reuben the firstborn of Israel. Though he was the firstborn, his birthright was given to the sons of Joseph son of Israel, because Reuben defiled his father’s bed. So he is not reckoned according to birthright. 2And though Judah prevailed over his brothers and a ruler came from him, the birthright belonged to Joseph. 3The sons of Reuben, the firstborn of Israel: 4The descendants of Joel: 5Shemaiah his son, Gog his son, Shimei his son, Micah his son, Reaiah his son, Baal his son, 6and Beerah his son, whom Tiglath-pileser king of Assyria carried into exile. 7Beerah was a leader of the Reubenites. His relatives by their clans are recorded in their genealogy: 8Jeiel the chief, Zechariah, and Bela son of Azaz, the son of Shema, the son of Joel. They settled in Aroer and as far as Nebo and Baal-meon. 9They also settled in the east as far as the edge of the desert that extends to the Euphrates River, because their livestock had increased in the land of Gilead. 10During the days of Saul they waged war against the Hagrites, who were defeated at their hands, and they occupied the dwellings of the Hagrites throughout the region east of Gilead.