Diplomacy is based off of the board-game "diplomacy":http://en.wikipedia.org/wiki/Diplomacy_%28game%29
Also, I define diplomacy on WarLight as the game in which the aim is to create strategical alliances in order to gang-bang strategically until eventually you either get destroyed yourself or destroy everyone else. Roleplay and diplomacy is not necessarily different. The clans which are referred to as roleplaying clans are usually referring to internal roleplay, not a setting of WarLight game.
Vote on the UserVoice to bring diplomacy into the game!