I love Diplomacy. The alliances, intrigue, negotiation, backstabbing, and the relatively simple mechanics that help emphasize the diplomatic aspect over the game mechanics.
However, it can be hard to find a group of people to play it with; not everyone likes such a cutthroat game, it requires 7 players (I hear you can do it with fewer, but that it's not as good), and it takes up a whole day to play.
Are there any good games that have a similar diplomatic and negotiation focus, but which play quicker, require fewer players or are more flexible in player number? A game will be a good fit if the diplomatic aspect of alliances, backstabbing, and the like is a substantial or the majority of the game, with less emphasis on individual strategy, tactics, and luck.