In your modern army (modern defined as dating from the 1500s onward), you've got three basic units: your company, commanded by a captain; your regiment, commanded by a colonel; and your army or division, commanded by (ultimately) the sovereign. In the past as today, the individuals who actually held these lofty posts, sovereign included, were often no-talent dweebs whose principal qualification was that they had clout, noble blood, or some unsavory combination of the two. Lest the army be massacred, those behind the scenes manuevered to have "lieutenants" (deputies) appointed to assist the nominal commanders. These lieutenants, lieutenant colonels, and lieutenant generals did much of the actual decisionmaking.