Its complicated to explain in words I think. But perhaps once the game is released we will be able to understand it better.
How I see it is, you will have two options
1.) the 2v2 regular multiplayer campaign
2.)the MMO type campaign map-(for custom created clans or "guilds" if u will)
In the MMO type campaign map, u and your friends "guild" appoint one person as a damiyo, and the rest become warlords. (I'm pretty sure i read it would be a max 8 players per team). You battle it out against other teams for 2 weeks at a time. Your Damiyo will make descisions on where to attack and what warlords to attack with. But Im not sure he can attack himself...Your aiming to gain strong footholds on the map, better resources, better units, I would assume. The teams who have more points, or some other kind of value that is greater, will advance up the Shogun clan "guilds" leader boards and move onto another MMO campaign map.
That's kind of how I understood it. It's really kind of vaguely described in these interviews. We really just need to see it in action I think.