Diplomacy is a strategic board game created by Allan B. Calhamer in 1954 and released commercially in 1959. It's main features from other board games are it's negotiation phases, where players talk to each other, forming alliances and other deals, and the complete lack of luck in the resolution of combat in the game. It has a wide player-base both online and in e-mail and even postal games.
Check the link below for detailed information on the game itself, including the full text of Richard Sharp's book on the game, The Game of Diplomacy.