Charles Ellicott Commentary Numbers 32:5

"And they said, If we have found favor in thy sight, let this land be given unto thy servants for a possession; bring us not over the Jordan." — Numbers 32:5 (ASV)

Bring us not over Jordan— These words may be understood either simply as a request that the inheritance of the speakers might be assigned to them on the eastern side of the Jordan, or, as they appear to have been understood by Moses, and as they were in all probability designed to be understood, as a request that the conquest of the western side of the Jordan might be left to the other tribes, and that the Reubenites and Gadites might be permitted at once to establish themselves in the land which had been already subjugated.

It is possible that the speakers, judging from the ease and rapidity with which the eastern side of the Jordan had been conquered, might have thought that their brothers were well able to subdue the western side without their aid. Be this as it may, their language indicated a selfish consideration of their own interests, and it was calculated to discourage and dishearten their brothers, and consequently it was strongly reproved by Moses. It is deserving of notice that the tribes of Reuben and Gad and the half tribe of Manasseh were among the first who were taken into captivity by the King of Assyria (1 Chronicles 5:26).