דברי הימים א, פרק ה׳, פסוק כ״ג

The establishment of the half-tribe of Manasseh on the eastern side of the Jordan River was defined by a massive territorial expansion. Driven by a surge in population, the tribe was compelled to widen its borders simply to accommodate its people [רד״ק, מצודת דוד, מלבי״ם]. Upon returning home from war, the men of Manasseh discovered that their original settlements could no longer hold them. To relieve the overcrowding, they expanded into the areas previously vacated by their brethren who had moved toward the region of the Hagrites [מצודת דוד].

This rapid growth was unique to Manasseh. Their population multiplied at a noticeably faster pace than the neighboring tribes of Reuben and Gad, requiring a much broader expansion into new lands [מלבי״ם]. Geographically, their new borders spanned from the Bashan area in the north and moved westward, reaching Baal Hermon, Senir, and Mount Hermon [ביאור שטיינזלץ]. Although the Torah traditionally uses the name Senir as a direct synonym for Mount Hermon, listing them as separate destinations indicates that different peaks and sections of this vast mountain range were identified by their own specific names [ביאור שטיינזלץ].