I’m interested in an easy-to-learn wargaming system that allows for tactical control of combat units within an army, such as a cavalry formation or a phalanx of spearmen.

And that probably describes a lot of them, but please bear with me. I’ve played several editions of D&D across several decades, so I’m familiar with running PCs, but I have zero experience with actual wargames that send armies or detachments against each other.

That said, what I’m looking for is a system that would allow several players to each control several combat units. I’m open to a broad range of time periods, say roughly 500-1200 or so.

Beyond this, I simply don’t know enough about wargames to ask in more detail. Osprey Publishing has a series of wargame books for a whole range of styles and eras, but I don’t know if their system is especially well-thought out or playable. Can someone help me get my bearings, and maybe find the right system for me?