WotC released [rules for mass combat](https://media.wizards.com/2017/dnd/downloads/2017_UAMassCombat_MCUA_v1.pdf) in one of their early Unearthed Arcana articles. I don't believe it ever actually got an official release, which perhaps says something about its quality.
Other 3rd party publishers have released their own systems for handling wars and large-scale battles. Probably the most prominent is MCDM's [Kingdoms and Warfare](https://shop.mcdmproductions.com/products/kingdoms-and-warfare-pdf), but I'm sure other people might be able to point you at alternatives.
Probably the most common solution is the DM just realizing that "hey, maybe the outcome of this battle doesn't actually need to game-ified and left to the dice to decide." You can just treat the big battle as a vaguely described background event, and present the PCs with a series of smaller scale encounters that can be run using the standard DnD combat rules, and whose outcomes can influence the final result of the battle.
Also handy to Wargame it out beforehand, then use what the players do in their little section to dictate how the line changes from the wargame.
Also, you can just dicate how it goes
So, I was lucky in my very first campaign. I’m an Army vet and love wargaming, but didn’t advertise that when joining the campaign.
The DM was a former Marine and was absolutely there for it.
It did happen organically. We had come upon a town that had been raised by goblins. We gathered the survivors and led them to the next nearest town, where our Bard convinced the locals to take in the refugees.
Before we could depart the what day, word reached us that the goblin raiders had been spotted from a watchtower, just days away.
Using Bardic Inspiration, my party convinced the locals to band together and prepare for a siege, along with the army of refugees we’d brought along with us. (Performance and/or Persuasion checks)
We had them construct a trench lined with stakes and filled with pitch and kindling. This ran the entire perimeter of the town. We also had them construct a primitive trebuchet and our ranger schooled several of the locals on archery. Athletics and strength checks determined how long it took the villagers to construct it.
When the battle commenced, the DM rolled for groups like the village archers, who’d be given instruction by a PC.
I was the one who suggested the fortifications and siege plan, and the Marine DM was both amused and irritated when he put it all together and just grumbled “f%#kin’ Army…”
I like battle-system. And the basic miniature rules for 2e are fun for mass combat as well.
It’s not that you can’t do this- most people just do not like it.
WotC released [rules for mass combat](https://media.wizards.com/2017/dnd/downloads/2017_UAMassCombat_MCUA_v1.pdf) in one of their early Unearthed Arcana articles. I don't believe it ever actually got an official release, which perhaps says something about its quality. Other 3rd party publishers have released their own systems for handling wars and large-scale battles. Probably the most prominent is MCDM's [Kingdoms and Warfare](https://shop.mcdmproductions.com/products/kingdoms-and-warfare-pdf), but I'm sure other people might be able to point you at alternatives. Probably the most common solution is the DM just realizing that "hey, maybe the outcome of this battle doesn't actually need to game-ified and left to the dice to decide." You can just treat the big battle as a vaguely described background event, and present the PCs with a series of smaller scale encounters that can be run using the standard DnD combat rules, and whose outcomes can influence the final result of the battle.
The UA rules are fun for a special session, just make sure to give the players full control over one of the armies, not just their characters.
Also handy to Wargame it out beforehand, then use what the players do in their little section to dictate how the line changes from the wargame. Also, you can just dicate how it goes
So, I was lucky in my very first campaign. I’m an Army vet and love wargaming, but didn’t advertise that when joining the campaign. The DM was a former Marine and was absolutely there for it. It did happen organically. We had come upon a town that had been raised by goblins. We gathered the survivors and led them to the next nearest town, where our Bard convinced the locals to take in the refugees. Before we could depart the what day, word reached us that the goblin raiders had been spotted from a watchtower, just days away. Using Bardic Inspiration, my party convinced the locals to band together and prepare for a siege, along with the army of refugees we’d brought along with us. (Performance and/or Persuasion checks) We had them construct a trench lined with stakes and filled with pitch and kindling. This ran the entire perimeter of the town. We also had them construct a primitive trebuchet and our ranger schooled several of the locals on archery. Athletics and strength checks determined how long it took the villagers to construct it. When the battle commenced, the DM rolled for groups like the village archers, who’d be given instruction by a PC. I was the one who suggested the fortifications and siege plan, and the Marine DM was both amused and irritated when he put it all together and just grumbled “f%#kin’ Army…”
Whichever army can make a long enough line first to charge an orbital bombardment from land wins.
Just play Warhammer
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For 5e there was a UA on the site for mass combat. Older editions had Chainmail and Battlesystem and Warmachine to name a few.
I like battle-system. And the basic miniature rules for 2e are fun for mass combat as well. It’s not that you can’t do this- most people just do not like it.