What does Joshua 12:6 mean?

Moses, the Lord’s servant, and the Israelites defeated these kings. Moses gave their land to the tribes of Reuben, Gad, and half the tribe of Manasseh. Joshua 12:6 - Modern Text Bible

(This land east of the Jordan was assigned to two and a half tribes, fulfilling God’s promise and setting the stage for Joshua’s conquests west of the river.)