Moses, the servant of the LORD, and the people of Israel defeated them. And Moses the servant of the LORD gave their land for a possession to the Reubenites and the Gadites and the half-tribe of Manasseh.
Joshua, or whoever else is the historian before he comes to sum up the new conquests Israel had made, in these verses receives their former conquests in Moses's time, under whom they became masters of the great and potent kingdoms of Sihon and Og.
Commenting on Joshua 12:1-6
Them did Moses the servant of the Lord, and the children of Israel, smite,.... That is, the inhabitants of those kingdoms they smote with the edge of the sword, and took possession of them, the history of which see in Num 21:1, and Moses the servant of the Lord gave it; the whole dominion of the two kings before mentioned: for a possession unto the...
Jos 12:6 These two kings were smitten by Moses, etc.: vid., Num 21:21., and Num 32:33.