The efforts to heal the fracture within the tribe of Judah finally succeed, resulting in a unified movement to restore the king to his rightful position. This dramatic shift in loyalty does not happen on its own but is the direct result of active persuasion.
Commentators differ on exactly who brings about this change of heart. One perspective suggests that David himself successfully sways the people through the messages he previously sent them [מצודת דוד]. Another view points to Amasa, arguing that he is the one working directly with the people to actively convince the men of Judah [רד״ק, ביאור שטיינזלץ].
Regardless of who leads the effort, the success of this persuasion is absolute. The entire tribe is swayed with remarkable ease. The collective change of heart happens so smoothly that it is as if only a single person is being convinced [מצודת דוד]. With complete consensus reached, the people reach out to the king with a clear request, asking him and all his servants to return to them [ביאור שטיינזלץ].