I'm curious to see if there is any interest out there in people participating in a mass combat...

I have my own system that seems to work well, and is based on the 3.5 rules. I normally use miniatures in RL with out a battle grid (Just using a measuring tape to figure things out... I guess kinda like Warhammer)
So for the pbp I was thinking about using a hex grid on the map, then the players would move their units around somewhat like chess.

If there is interest I will post some more on the rules I use.

Might need a little more info on Setting

Well D&D 3.5 character rules... Medieval Fantasy setting...

I was going to make up a country/region map, then each hex/square on that map will have a corresponding detailed map which would be used for the battle map...

If there is some other question you have about this idea, just ask

InnMates usually like to know what the Setting is, especially with a lead-in scenario to set the stage with a bit of background story to set the hook so to speak.

You mentioned Units, so what type of Units are you talking about and what Races ???

What is the Conflict ???

Well.

Think of it as though each person was a lvl 12(ish) character with the leadership feat, and a decent leadership score.
Each player has to equip and organise the Followers they get into units for battle. (Each unit would be identically equipped for ease of combat)

If there is some interest then there would be a monthly budget they would get for equipping and paying their troops.

As for story and why they are fighting... I haven't gotten that far yet. Wanted to judge the interest first