Establishing diplomatic relations with rival factions has always been a integral part of any turn-based strategy game. Much of the Sins success comes from being able to translate gameplay features that work well in turn-based games into real-time strategy. In doing so, the game takes a very unique approach to diplomacy with this expansion. Victory is measured through a diplomatic score, which gains or loses points in accordance to how well you get along with other factions. A whole new tech tree is included with Diplomacy, giving players a chance to bolster their economy, their firepower, or manipulate factions into fighting each other. This being the case, the best way to play Diplomacy is on maps that support four or more players. It takes some time to get a handle on how politics works and how to use it effectively. Since nobody likes you at the start of a match, and gaining any sort of trust is an uphill battle especially with races that are pre-disposed toward hating yours. However, fighting to get ahead is typical of the Sins experience. On the bright side, factions of the same species lean toward liking you, but not for very long. Winning over any of the opposition will involve doing completing missions for them. Other ways to gain influence include sending envoy units into an opponent's system and have talk on your behalf and paying them off outright.

There's the expected features, like researching trade agreements, exchanging ship or planet vision, and giving resources to allied factions. However, the real strength in Diplomacy comes from manipulation. With Diplomacy, players have the ability to issue missions to other factions, as computer controlled players have been able to do since the original game first launched. By offering up a reward, players can entice other factions invade a territory or weaken a rival by ordering a certain number of ships destroyed. At the same time, these custom missions will help improve relations between factions. If rewarding other factions (and potentially making them stronger) doesn't appeal to you, there's the option to go behind their backs and pay off the ever-present Space Pirates to raid the faction of your choosing. In preparation for the new clientele, the Space Pirates are stronger than ever before and if players are willing and able to shell out enough money, they can put together a sizeable force that can seriously ruin someone's day. With enough funds, players can gather a pirate force strong enough to wipe out all opposition in a territory. This is in addition to the normal Pirate countdown, where players factions bid against each other so that they will attack the one with the highest price on them.

The level to which Diplomacy influences the dynamic of how Sins is played can be subtle, but the effects ripple out to all parts of the game. Rivals will spend their time and resources going after the faction they dislike the most, so you can potentially avoid a lot of hassle if you manage to stay off the top of the hate lists. As they fight each other, you have a chance to develop your own strength and technology, which is actually a lot harder than it sounds. Players looking to win a diplomatic victory still need to invest in a sizeable army to take over territories and expand their empire in order to generate a strong economy. In other words, even a great mastermind needs to be backed by a powerful fleet of ships.

Diplomacy brings a number of other gameplay enhancements to the table, including speed controls so players can individually customize the rate of research, diplomatic rating, revenue or how fast the ships move. This helps greatly to improve the game's pacing, which is generally slower than most other real-time strategy games. There's also a new level of AI difficulty that takes things to the extreme. Even long-time Sins veterans will find a formidable challenge. All that said, Diplomacy mainly benefits the single player and human vs AI match experience. An AI player is guaranteed to carry out a mission with the agreed upon price and its behavior and attitude relates directly to the diplomatic score. Then again, a human player could suddenly turn around and stab you in the back, which might appeal to some people.

With Entrenchment, players strengthened defensive positions with powerful starbases. Diplomacy compliments the previous micro-expansion well, and provides a richer Sins experience. It also gives players the satisfaction of winning an economic victory without actually having one. Hiring pirate mercenaries to go in and soften up a planet (if not wipe it out altogether) has a certain satisfaction, and it certainly keeps you on your toes, since the same method can be used on you. Our major complaint is that factions will suddenly hate for no reason, even if you've spent the whole game ignoring them. This is likely because the computer worked to build up relations with other factions, which automatically bumps you up the crap list. Besides opening up the relations tree and guessing which faction hates you the most, it's almost impossible to figure out which one is gunning for you. Also, the option to bribe rivals with money and resources unlocks a little too far down the tech tree, and they don't work if the faction is already on the offensive.

Diplomacy adds a whole new layer of strategy, and it's a lot to get used to. It significantly turns up the need to multitask, but at the same time, players are presented with new and powerful tools to expand their empire. Picking up the add-on and turning the game into Trinity makes for deeply challenging gameplay, and is definitely completes the Sins experience so that players have more variety in how they choose to conquer the galaxy.