ACKS Domains At War: Battles has you covered if you're strictly looking for a mass combat system. It
is fairly crunchy, and can be played as a stand-alone hex-and-chit wargame.
It's designed for ACKS, itself a B/X (and LL) variant fine-tuned for high-level antics like running fiefs and building kingdoms and breeding monsters and stuff. But the Battles supplement, which deals with the actual mass combat system, should integrate seamlessly with just about any edition of TSR D&D (and maybe even the WotC ones too).
Campaigns, which deals with the nitty-gritty of raising and managing armies, works off of ACKS' uniquely consistent modeling of pre-industrial fantasy economics.