The game of Diplomacy was developed by Allan B. Calhamer while he was a student at Harvard Law School during the 1950's. While only a minor commercial success, Diplomacy has a small, devoted fanbase. Many famous politicians have stated that Diplomacy was their favorite game. John F. Kennedy and Henry Kissinger were both fans of the game, as was news anchor Walter Cronkite.
The major difficulty for playing the game is finding the seven players required. The game also takes a very long time to complete--usually three to six hours, or even longer if time for diplomacy is not capped. Although face-to-face diplomacy provides a more nuanced and exciting game, as players can actually see the discussions between two powers, if not overhear them, the difficulty of finding seven players in one's area has made mail, and now e-mail, the two most popular ways to play Diplomacy.
There has been a push in the past decade for better Artificial Intelligence for the game. Computers continue to improve, and have even become pretty good at no-press variants of the game, but cannot yet compete with humans in games with communication.
Diplomacy is a zero-sum, turn-based, strategy wargame played by seven people, each taking the role of a Great Power in Europe during the World War I era. The seven countries are Austria (or Austria-Hungary), England, France, Germany, Italy, Russia, and Turkey. The game year is divided into five phases: Spring movements and retreats, Fall movements and retreats, and Winter adjustments. Each power controls only two types of units: armies and fleets. Fleets can occupy ocean spaces and coastal provinces, and can convoy armies across ocean spaces. The board is divided into 75 spaces, 56 land and 19 sea. 34 land spaces are called supply centers. Powers capture supply centers by having their troops occupy the territory after fall retreats. Powers maintain ownership over every province they have conquered until another power is able to move one of his or her own units into the province during the fall (although keeping track of the ownership of non-supply center provinces is essentially irrelevant). Owning more supply centers than units after the fall retreats allows a player to build a unit in one of his or her unoccupied home centers during the winter adjustments. A player wins by taking 18 supply centers. Achieving solo victory is extremely difficult, and most games end in draws ranging in size from two to four players.
Diplomacy is played on the board showing the political map of Europe immediately prior to World War I. Diplomacy has a very subtle and complex geography, with criss-crossing stalemate lines from east to west, north to south, and in corners. Geography is an important factor in determining a country's winning strategy--Turkey will never view England as an objective for conquest except in extraordinary circumstances. More important, however, is diplomacy. A loyal ally will work around geographical conflicts to find a mutually satisfactory solution.