Numbers 32:33

And Moses gave unto them
By word of mouth, in the presence of the court, or rather by some instrument drawn up and signed by him and the sanhedrim, or witnessed by them:

[even] to the children of Gad, and to the children of Reuben, and unto
half the tribe of Manasseh the son of Joseph;
no mention is made of this half tribe joining with the other two tribes in the request to settle on this side Jordan, and therefore it is generally thought that they were encouraged, by the success of the two tribes, to make a like motion; or else Moses and the princes, observing that there was too much land for the said tribes, joined this half tribe with them, the land being suitable for them:

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;
of which kingdoms, and the conquest of them, see ( Numbers 21:24-35 ) , and several of the cities in them are after mentioned.