IMHO it starts with the group of operational functions (command, sense, act ...) That leads to categorizing army components into categories - this does "act", that does "sense" etc. That leads to the evaluation (in tight fiscal situations) of trying to see where there is overlap that can be rationalized by combining. The whole thing was then topped off by a major PY need for CMTC and some other roles, the current operational roles (Bosnia with a high rifle platoon, low arty and tank requirement). Before you knew it you had folks trying to carve out a role to stay relevant - tankers as "THE" direct fire bunch - combining MGS, ADATS and TOW UA; engrs as the construction guys for everything; arty as "ALL Things" indirect fire; and a logistics system unleashed as national support elements working out of FOBs. On the side you can throw in the attempts to get every sense function grouped under ISTAR and All-source intelligence centres.
You then bring in the concept of "building blocks" of a little act here, and a little sense there, and a slice of command over there. Before you know it you are building "tactical self sufficient units" (which morph into the "optimized battle group" - a set of preassembled building blocks) and JIMP brigades.
Like I said - a whole different level.