“Now these are the kings of the land, whom the Israelites defeated, whose land they occupied beyond the Jordan toward the east, from the Wadi Arnon to Mount Hermon, with all the Arabah eastward. King Sihon of the Amorites lived at Heshbon. He ruled from Aroer, which is on the edge of the valley of the Arnon, and from the middle of the valley as far as the river Jabbok. The boundary of the Ammonites was half of Gilead and the Arabah to the Sea of Chinneroth eastward. This is in the direction of Beth-jeshimoth, to the sea of the Arabah, the Dead Sea, southward to the foot of the slopes of Pisgah. King Og of Bashan, one of the last of the Rephaim, lived at Ashtaroth and at Edrei. He ruled over Mount Hermon and Salecah and all Bashan to the boundary of the Geshurites and the Maacathites. He ruled over half of Gilead to the boundary of King Sihon of Heshbon. Moses, the servant of Yahweh, and the Israelites defeated them. Moses, the servant of Yahweh, gave their land as a possession to the Reubenites, the Gadites, and the half-tribe of Manasseh.”
This is a Deuteronomic summary of what happened. Basically, there were two kings east of the Jordan, kings Sihon and Og, while there will be thirty-one on the west side of the Jordan. Moses led the attack that led to the capture of these two kingdoms. This land was split up between the Reubenites, the Gadites, and the half tribe of Manasseh.