Sins of a Solar Empire: Diplomacy is the second expansion pack for the Sins of a Solar Empire video game. It was released on February 9, 2010. The game requires the main game and the first expansion pack for it to work. In this game, the player is a leader of a civilization involved in a galactic war and the goal is to manage the empire and command the player’s starships to survival and victory. The main game, Sins of a Solar Empire, offers diplomacy options that enable the player to forge or break alliances as well as place bounties on opponents/allies. This expansion pack extends the diplomacy mechanic of the game. There are also some major changes as well as added features.
One of the main changes this game is the Relationship System. It added a Relationship bar that considers every aspect of the player’s relationship with other races and players. This enables players to donate resources, issue pacts and issue missions to alliances. The game also added a new envoy/pact system, wherein deploying of specialized cruisers is now possible. This helps improve relationships with other races as well. Aside from issuing missions to alliances, players can also now offer missions to pirates in exchange for a sum of credits.
Aside from these changes, this expansion also offers some additions to the original game. For instance, players can now select the maximum number of players allowed to win in certain conditions of allied victory. Two AI difficulties have also been added (i.e. Vicious and Cruel). There is also a new faster speed option.