2-1. As the Nation’s decisive land force, the Army provides a mix of headquarters, units, and capabilities to geographic combatant commanders (GCCs) in support of a theater campaign plan (TCP) and specific joint operations. In order to effectively command these organizations, the Army provides an echeloned array of higher headquarters designed toward a specific function or mission. Winning in large-scale ground combat requires Army forces that can integrate landpower in a multi-domain approach to defeat enemy forces and control terrain. The theater army, corps, and division headquarters give the combatant commander several options necessary for the employment of landpower. (See paragraphs 2-4 through 2-103 for a discussion of Army echelons.)