There are four total factions in the galaxy of Sins of a Solar Empire. Three of these factions are controllable by the player: the industrious Trader Emergency Coalition (TEC), the psychic Advent and the technologically advanced Vasari. The fourth faction, the Pirates, are an NPC faction that exists only to collect bounties by destroying ships of the other three.
In the Sins of a Solar Empire: Rebellion stand-alone expansion, the three factions have fractured into Loyalist and Rebel camps, that have different philosophies and take very different stances on their enemies.
Main article: TEC
The Trader Emergency Coalition (TEC) was originally a group of trade worlds that descends from earlier human exploration, in the "Golden Age" their economy flourished and society grew. At one point they cast out the Advent, a religious desert sect that the Traders despised (see Advent) which lead many to mark the end to the Golden Age. In recent times the Vasari entered the scene as they fled from their Xeno enemy. To defend against the Vasari, the Traders formed the TEC, mobilized their economy towards military production and managed to hold the Vasari off by converting their merchant vessels and mining ships into warships, and later produced the Kol capital ship which was their first battleship design in 750 years. The Advent then returned, having become much more powerful, and started a two-front war. This compelled the TEC to force retired veterans to return to the navy to fight back the Advent. The TEC tends to have heavily armored units and mostly focus on ballistic weapons (missiles and cannons) and less on lasers. TEC ships are heavily armored, shielded, and have greater hull strength than the ships of any other faction in the game, though this staying power often comes at the price of less firepower and damage-dealing potential. The TEC have a mixed close-to-long range arsenal but mostly focus on the latter. Their preferred planets are terran planets.
TEC have some of the least expensive frigates and cruisers of any faction, enabling them to more easily build large fleets and overpower enemies with sheer numbers. The Javelis LRM Frigate has the longest range of any combat unit in the game and delivers very high firepower for its cost, making it one of the most dangerous assault units in the game. On the other hand, the Hoshiko Robotics Cruiser is a defensive support unit that acts as a mobile repair bay and keeps your fleet intact during intense firefights. Both of these units are very inexpensive to build, are very cost-effective, and available early in the game. This gives TEC a potent early-game fighting force. Their capital ships also shine in the early game, with the Sova Carrier, Marza Dreadnought, and Akkan Battlecruiser performing well in their respective roles. A swarm of Javelis LRM Frigates backed up by Hoshiko Robotics Cruisers and two Sova Carriers can be a difficult force to defend against, and a good TEC player can field it within the first 20 minutes of the game. This makes TEC arguably the best rushing faction. The Argonev Star Base's ability to self-destruct can antagonize even the best of players; they have no way of knowing whether they're walking into an explosive trap, and usually are forced to keep their distance just to be safe. The TEC have the strongest capital ships in the game in terms of health and armor and, in general, a TEC player will enjoy exceptional survivability on all their ships.
On the economic front, the TEC have a powerful advantage if they lead with the Akkan Battlecruiser. This gives them an edge in the early colonization phase of the game, both bolstering the resource producing of newly colonized planets as well as reducing your dependence on slow and expensive colony frigates. Their Civilian Tree also has several useful and inexpensive technologies. Although TEC does get Trade Ports earlier than other factions, this advantage is not as big as it first appears; in practice, it is easy to maintain a competitive economy without trade in the first 20 minutes of the game, giving the other factions plenty of time to build the additional labs necessary. Late game, the TEC receive an upgrade called Pervasive Economy that gives them unrivaled economic power.
Although TEC opens with powerful military units, its late game prospects are not nearly as good (despite this they are still more than capable of holding their own late in battle). While they retain a very cost-effective Kodiak Heavy Cruiser and the starbase-smashing Ogrov Torpedo Cruiser, the military situation grows increasingly grim. TEC has very little answer to powerful late-game abilities like Repulsion and Distortion Field that can completely shut down portions of the enemy fleet, and virtually nothing that can protect their capital ships against the massive amount of firepower the enemy will be capable of throwing at them. TEC capital ships begin to suffer for another reason as well; they offer fewer fleet support abilities than their Vasari and Advent counterparts, and need to lean on powerful level 6 abilities to compete. Taken together, TEC is a faction that must find an advantage in the early game and carry it forward. They begin to fall behind the other factions on every front except economy, and will need to maintain better capital ships and a significantly larger fleet to compete.
TEC Loyalists are a defensive variation on the traditional TEC formula. With Twin Fortresses, the TEC Loyalists can build two Argonev Star Bases at a planet instead of one, and five Argonevs at a star instead of four. The TEC Loyalists can also access Novalith Cannon with six Military Labs instead of eight. One advantage of the loyalists is their economic prowess allows them to become diplomatically allied with other races; something the xenophobic rebels find much harder to do.
TEC Rebels are an aggressive variation on the traditional TEC formula. With Pirate Mercenaries, the TEC Rebels can spawn controllable Pirate ships at their planets. With Truce Amongst Rogues, the Pirates and Militia ally with the TEC Rebels.