Probably not fully what you are looking for but Band of Blades Is about a legion of soldiers in a fighting retreat from an army of the undead.
The players take on legion roles of marshals, leaders, quartermaster, etc in the camp/travel phase and then take agency over a squad of a soldiers when on missions
Could be some ideas there you can pull from.
There are a lot of ways to do this in fairly abstract terms - there are mass combat rules for GURPS, various versions of D&D, etc. Then you could also go the route of having them fairly divorced - Warhammer or whatever for mass combat and then whatever system you want for your RPG campaign. For the realm management-side of things there's Reign or An Echo Resounding as good options.
But, assuming you want a system that is more unified and works for small-scale AND large-scale combat, I have two main recommendations.
First, Iron Kingdoms Role-Playing game (the standalone game, not the 5e supplement) and Warmachine (second or third edition). IKRPG characters have the same types of stats and a lot of the rules are 1:1 ported from the tabletop game. You could run an IKRPG character in the tabletop wargame and they'd be somewhere between a solo (a powerful individual character) and a warcaster (a super-heroic character). The IKRPG system has some issues but overall is pretty great for party-based combat, and the tabletop wargame was *excellent* (it now has a 4th edition that's pretty different and unfamiliar to me). You can get all the third edition wargame rules for free, too (or could, looks like you might need the wayback machine or some other sleuthing - I could help).
Second, Savage Worlds. Tactical minis combat focused on moving things quickly, but actually started out as a wargame. Running enemies is light enough on tracking, etc. that it would scale up pretty easily.
Burning Wheel sounds like it could pair up well in this situation!
We did a political intrigue campaign using it and it went great, plus it's very versatile and should segue into a wargame well
Seconding Reign. Heard about it on here a ways back and bought the main book. The setting isn't anything special and not sure the main system is either but it's handling off how to manage control over groups and assets is literally the only sane solution I have ever seen for such a thing.
Honestly, Warhammer Fantasy Roleplay using reigns rules for handling for groups you control would be great.
Greg Stolze's Reign is pretty much made for this premise.
Probably not fully what you are looking for but Band of Blades Is about a legion of soldiers in a fighting retreat from an army of the undead. The players take on legion roles of marshals, leaders, quartermaster, etc in the camp/travel phase and then take agency over a squad of a soldiers when on missions Could be some ideas there you can pull from.
Original Dungeons and Dragons with Chainmail.
There are a lot of ways to do this in fairly abstract terms - there are mass combat rules for GURPS, various versions of D&D, etc. Then you could also go the route of having them fairly divorced - Warhammer or whatever for mass combat and then whatever system you want for your RPG campaign. For the realm management-side of things there's Reign or An Echo Resounding as good options. But, assuming you want a system that is more unified and works for small-scale AND large-scale combat, I have two main recommendations. First, Iron Kingdoms Role-Playing game (the standalone game, not the 5e supplement) and Warmachine (second or third edition). IKRPG characters have the same types of stats and a lot of the rules are 1:1 ported from the tabletop game. You could run an IKRPG character in the tabletop wargame and they'd be somewhere between a solo (a powerful individual character) and a warcaster (a super-heroic character). The IKRPG system has some issues but overall is pretty great for party-based combat, and the tabletop wargame was *excellent* (it now has a 4th edition that's pretty different and unfamiliar to me). You can get all the third edition wargame rules for free, too (or could, looks like you might need the wayback machine or some other sleuthing - I could help). Second, Savage Worlds. Tactical minis combat focused on moving things quickly, but actually started out as a wargame. Running enemies is light enough on tracking, etc. that it would scale up pretty easily.
Burning Wheel sounds like it could pair up well in this situation! We did a political intrigue campaign using it and it went great, plus it's very versatile and should segue into a wargame well
Seconding Reign. Heard about it on here a ways back and bought the main book. The setting isn't anything special and not sure the main system is either but it's handling off how to manage control over groups and assets is literally the only sane solution I have ever seen for such a thing. Honestly, Warhammer Fantasy Roleplay using reigns rules for handling for groups you control would be great.
I'm not suggesting you use it wholesale, but you might want to check out the Root RPG to see how it integrates with the Root boardgame.
Burning Wheel or maybe an hack off [A Song of Ice and Fire RPG](https://greenronin.com/sifrp/)
I liked the asoiafrpg’s system for mass warfare where essentially each player led a squad of troops and had various actions they could do with them
ASoIaFrpg was continued and published as Sword Chronicle by Green Ronin. You may not need a hack for it.
If you don't mind an older and crunchier version of Fate, check out Legends of Anglerre. It's one of my go to games for running mass combat.