Half the tribe of Manasseh are here added to the tribes of Reuben and Gad, either because upon the good success of the two tribes of Reuben and Gad, they were encouraged to make the same request for themselves, as having much cattle as well as they; or because upon further consideration it was found that this portion of land was more than sufficient for those two tribes; and it was given by Moses to these rather than to any other, because they fought against the Amorites with great courage and success, here Numbers 32:39 Joshua 17:1.
Related Commentaries of Numbers 32:33
Numbers 32:33
33 And Moses gave unto them, even to the children of Gad, and to the children of Reuben, and unto half the tribe of Manasseh the son of Joseph, the kingdom of Sihon king of the Amorites, and the kingdom of Og king of Bashan, the land, with the cities thereof in the coasts, even the cities of the country round about.