The tribes of Reuben and Gad came to Moses and asked to get possession of the land on the eastern side of the Jordan River. This is part of the Land of Israel but not within the Land of Canaan. The Land of Canaan does not share any borders with a foreign population. To the south is a desert, to the west is the sea, and to the north at the time there were the forests of Lebanon, which were not populated. And what about the east? If the tribes of Gad and Reuben had taken land to the west of the Jordan River, the eastern bank would have remained empty after the destruction of the kingdoms of Sihon and Og. This would have served to separate between Israel and the other nations. Then Israel would have lived in Canaan in something of a bubble which had no direct contact with the rest of the world. The link between Israel and the other nations passed through the strangers (the initials of Gad and Reuben, G.R., spell out the word "ger" – a stranger). Reuben and Gad, sons of Leah, take upon themselves the task of being a bridge to the rest of the world, and they get close to the borders with Ammon and Moab. The link between Israel and the rest of the world is through trade, and it is therefore clearly emphasized that the tribes want to obtain the eastern bank of the Jordan for economic reasons.
Following instructions from G-d, Moses agrees to the request of the children of Gad and Reuben. But then, suddenly, something novel appears. The northern section on the eastern side of the Jordan also becomes available for Israel to settle, and Moses gives the area to parts of the tribe of Manasseh, which were not included in the original request. One part of the land is given to Machir, son of Manasseh, who must have been at least 180 years old. Yair, son of Manasseh presents us with a similar quandry. How can we understand this?
The solution to our dilemma can be found in the book of Chronicles (I, 2:21). There it is clear that the Bashan area was captured by children of Manasseh during the time of Joseph, and they continued to rule there through the time of enslavement in Egypt. Gashur and Aram captured from them the sixty cities which went by the name of the Villages of Yair. (In their memory, the same name was given to the cities of Yair in the Gilad area, as is noted in the book of Judges.)
In this week's Torah portion, Moses gives the land back to the descendants of Manasseh, as is indicated in the Torah portion of Massei (Numbers 34:14): "The tribe of the sons of Reuben, by their fathers' houses, and the tribe of the sons of Gad, by their fathers' houses, took possession" – in response to their request. However, "Half of the tribe of Manasseh took their heritage" – this belonged to them from the beginning.