"Sins of a Solar Empire: Diplomacy" expands upon the Diplomacy mechanic. The relations system is more visible, and players can give missions to each other, as opposed to the original's NPC-only mission issuing. Diplomatic envoy cruisers can be used to further improve relations, and the researchable pacts can significantly strengthen both sides of the alliance. The expansion also sees a noticeable increase in pirates' strength, and their bases are now outfitted with mines and TEC-issue repair platforms and strike craft hangars.