The half of the tribe of Manasseh, along with Reuben and Gad, had their territory assigned them by Moses on the east of the Jordan (Numbers 33), but this was done after only Reuben and Gad had asked to receive their inheritance eastwards of the Jordan river.
1 Now the children of Reuben and the children of Gad had a very great multitude of cattle: and when they saw the land of Jazer, and the land of Gilead, that, behold, the place was a place for cattle;
2 The children of Gad and the children of Reuben came and spake unto Moses, and to Eleazar the priest, and unto the princes of the congregation, saying, [..]
5 .. if we have found grace in thy sight, let this land be given unto thy servants for a possession, and bring us not over Jordan. [..]
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. (KJV)
Why was half of the tribe of Manasseh also stationed on the east side of the Jordan? I don't see this tribe asking for this portion of the land.