Themken: I remember playing Cossacks, a twenty-five year old RTS game, in co-op mode. I think it was only two per team though but not sure as I have stuck to single-player for twenty years.
Atlo: I'm reasonably sure you are mistaken... it did have co-op; but not the ''
One dude could be in charge of erecting buildings, another could be in charge of collecting minerals, the next takes care of the army, and so on.'' OP is looking for...
Reason: I used to play that game in multiplayer and I'm pretty sure I would remember if it had such a feature.
Also: GOGO Poland! Pikemen that cost only food & wood vs metal in 95% of all other factions. Winged hussars - heavy cavalry, but fast as light cavalry... Overpowered faction IMHO... yet in competitive games most picked Ukraine & Algeria for some reason. :/
I do not have any Cossacks game installed at the moment but this is straight from The Art of War manual:
"Players of the same team can select the same colour in a multiplayer game. This means
they will play for the same nation ("Two-in-one-Nation"). Note: This mode is particu-
larly useful if players are planning to share the responsibility. Thus, one player could man-
age resources and matters of state while the other takes control of the military."
I also like Poland as they are strong early.