[quote=@Zugzwang]
as I mentioned briefly, 99% of the time on campaign, soldiers are not fighting. Most of soldiering is walking, cleaning, cooking, watching for the enemy, and so often doing a whole lot of nothing. This ratio has changed over time, obviously, with the most fighting per day likely in the Wars of German Unification or perhaps in the invasion of Europe in 1944-5, but the principle has never been inapplicable.
[/quote]

No, the ratio hasn't changed much. The bulk of a lot of military operations is non-combat duty. You not only have the principles of cleaning and cooking to take care of to maintain a basic level of humanity but you have the management of a large logistics framework requiring truck drivers moving porta-potties from point A to point B, medical personnel overseeing not only for the care of soldiers behind enemy lines but civilian casualties, intelligence gathering which'd be a lot of radio interception, translating, code-breaking, and finding informants without necessarily going out into the field to kill anything. You have communication operations to organize where what report goes where. Civilian operations to keep the occupied territories at least a little happy and to ensure the right information goes back home so the civilian population supporting you gets the right information.

You need people to keep security, sitting over a FOB or some deployment position to make sure that not only do people not break in to cause problems but the young privates that just came in from basic don't get drunk and bored and steal from the cantina. And then you have basic military administration with all of the non-combat field work funneling into central command where it's processed centrally with people running accounts, managing liasons with national or foreign news, and so on and so on before it hits the commander.

At the end of the day the combat duties of the entire army is rather minimal. But really: this sort of structure was not around all the time and it wasn't until Napoleon and his Grand Army that this structure that this system came into place. Prior, more men may have been devoted to combat duties than non-combat duties and would have operated in a less ideal matter. Under the Napoleonic structure you get less combat personnel but the administrative structure makes a single soldier fight with the capabilities of ten men by relieving the stress of having to do multiple functions on his own (supplying his own gear, which was the norm in medieval armies for instance; that's now all handled through the quarter master and his clerks).

So while maybe you're not always fighting in the field back then and even now: there's far few people devoted to actual combat roles than there was two-hundred years ago but doing their combat a lot more effectively.

Before Napoleon often who commanded what was up to negotiations between the commanders or even the nobility (in the context of the middle ages) but that was rarely in bureaucratic management, it was more in what part of the army they were to lord over (center, right, left flanks for basic terms) and who got what or did what during or after the fact.