Following the successful military campaigns against the kings east of the Jordan River, the national focus shifted from physical conquest to permanent settlement and the distribution of land. Taking possession of this territory meant more than merely winning battles; it involved firmly holding the land, dividing it, and establishing permanent homes [מזרחי, רש״ר הירש, ביאור יש״ר]. This initial distribution of territory was unique because Moses executed it immediately on his own. He did not wait for the formal lottery system involving the Urim and Thummim and the tribal leaders, a process that would later be required for dividing the Land of Israel itself [מלבי״ם].
A careful review of the historical record reveals an apparent gap between the vast expanse of the conquered territory and the specific portions granted to individual tribes. The primary approach among commentators is that the historical account employs a concise style, implying that the land which was conquered at that time was then distributed to the tribes of Reuben and Gad [רמב״ן, בכור שור, חזקוני, הטור הארוך]. Alternatively, the act of taking possession in this context can be understood as an act of bequeathing, meaning the land was directly transferred into the ownership of these tribes [הכתב והקבלה].
Other commentators draw a clear distinction between the total conquered area and the specific tribal grants. In this view, the initial record of the conquest refers to the massive stretch of land from the Arnon River all the way to Mount Hermon. However, the specific gift to Reuben and Gad was limited to the southern region, starting from Aroer near the Arnon River by the Moabite border [ביאור שטיינזלץ]. Consequently, while the Israelites conquered the entire region up to Hermon, Moses only granted Reuben and Gad the southern half of the Gilead mountain range, reserving the northern remainder for half the tribe of Manasseh [רש״י, מזרחי, שפתי חכמים, גור אריה]. The decision to grant them only half the mountain was practical, as the entire territory was simply too large for their population [ביאור יש״ר]. Ultimately, this specific region was awarded to them as a gift to accommodate their massive herds of livestock [אברבנאל].
Beyond the practical distribution of territory, settling the eastern side of the Jordan River carries a subtle historical rebuke. Establishing tribal territories outside the borders of the Land of Israel was an indirect consequence of the sin of the spies. Had that tragedy not occurred, the Israelites would have entered the Land of Israel directly, conquered it, and divided it equally among all the tribes, leaving the settlement of the eastern bank for a later time. Furthermore, the eastern side of the Jordan possesses a lesser degree of holiness than the Land of Israel itself, a spiritual reality that eventually diminished the region's spiritual vitality and dedication to Torah study [העמק דבר]. From a literary standpoint, detailing the inheritance of Reuben and Gad and then immediately transitioning to the territory of the half-tribe of Manasseh follows an ancient structural rule. The narrative deliberately resumes from the exact geographical point where the previous description concluded, creating a seamless geographical and literary flow [ברכת אשר על התורה].