In my games and others, I've seen a fair amount of "Modernisms."
These are things that seem basic and standard to a modern audience but which actually post-date the game period.
I'll do a short series on the ones I notice in my game.
The Front Lines
Thinking of war as having "front lines" and a "rear area" is a fairly modern concept. World War I, mostly. Armies arrayed against each other will have lines, but those lines eventually play out on the fringes. There isn't a clear "our territory guarded along the edge byour troops vs. theirs guarded along the edge by theirs."
Armies march around, and chose to give battle or refuse it. In pre-modern forces, it's hard to force your opponent into a decisive battle if they don't want to give battle. Territory is taken and held and given back up as you move, or smaller forces are broken off to hold important points as the main force moves off to force battle.
Pretty much, to fight effectively you have to arrange your army to fight. You can march faster than you can arrange yourself to fight. Your opponents have basically the same speed as you. This means if you show up and then start to arrange yourself in battle order and your foe isn't interested in fighting, they can pack up and march off, screened by some light forces. So battles between similar forces are more mutual agreements to have it out. You can force your opponent to agree by putting them onto some other timetable - reducing the available food so they can't just march away and re-supply, raiding their baggage in previous battles and stealing their paychests, etc.
Magic changes battle, for sure, but it doesn't really mean total war with lines extending from impassable geographic end to impassable geographic end.
Up next: Absolute Monarchs.