If you don't know what diplomacy is...
here are the official rules
Basically it is the same idea as risk but without dice. You pick one of the 6 major powers in WW1 and battle with land and sea units. Each unit moves once per turn and can attack or defend. Two units attacking is a support. The fun part is before each turn you discuss your moves with anybody. You make deals, conspire against people, and lie about everything if you choose. then everyone writes down a move for their units. Whoever captures the world wins. In some ways it reminds me of that one game.
This is a game that should be arranged to be played, at least my opinion. I'd have to find a board for it but can run it through pms and all that jazz if anybody is down.