Follower of the Way
For myself, high medieval/early Renaissance large pitched battle. One side or both may have cannons. Both definitely have cavalry, infantry, irregulars, archers, siege weaponry, etc. Some battles are on the field, some are sieges, some are more complex affairs involving terrain manipulation and exploitation.What do people think of when they think of war in this context?
On the logistical side, we're talking less than a million total soldiers on both sides. The economic advantage is centered on land, as these societies are pre-industrial, and thus more land = more productivity, not having crossed the infrastructure and education barrier where land alone ceases to be the primary driver of economic activity. Materiel mostly consists of kit and food, less so ammunition, but sappers and military engineers would require more specialized support.
The Wars of the Roses are probably on the early end in terms of historical equivalents (though I would say some battles from the days of ancient Rome and Constantinople are also good inspiration), while the Napoleonic Wars are probably the most recent I'd allow for a typical D&D pseudomedieval setting. (Something like Eberron, for example, can obviously take all the way up to WWII.)
In terms of the actual events most likely to be seen by players? Mostly battle aftermath and special operations while battle is going. Briefing and debriefing. Some amount of the politics and jockeying of war (a thing popular history tends to downplay). The grim realities of war, not just on the field of battle, but in the home, on Main Street, in the churches and the grocers and the schools.