Late 1e (or during 2e? I forget) TSR put out Battlesystem, which was intended to cover just this type of thing.While that's fair, no edition of WotC D&D has included mass combat rules in anything remotely like the core rules, and AIUI they weren't core in any TSR edition either (but I welcome correction if I am wrong.)
It's clunky as all hell, but could probably be made to work. I dreamed up my own system years ago but have yet to give it a run-out; and the one time I was a player in a D&D game that turned into army-vs-army we made up the rules kind of on the spot and they worked surprisingly well.
I've a sneaking hunch that the Birthright setting (TSR, 2e) might include some rules for mass combats as well, it's ages since I looked at it.