I suppose a short faction primer would be in order.
The Core Worlds Confederation
Based around Terra Sector (of course), the Confederation is the most recent in a string of governments lasting just over a millenium. It also appeared the most stable, with the lowest-recorded number of military incidents per year, until a number of ambitious proposals were passed that threatened the borders of the Rim worlds. The situation has rapidly deteriorated, and is now on the brink of exploding into all-out war.
Confederation vessels are above-average in shielding and manuverability, and almost all of their capital ships feature Mass Drivers, magnetic accelerators capable of firing torpedoes, superdense metal slugs and remote-guided gun drones at several times Terran escape velocity.
The Outer Rim Alliance
History has shown that colonies are like children to their parent nations - and many parents are reluctant to easily release those they raised. This is how the Alliance came about, attempting to "free" themselves from the not-so-united Terran Union of old. The Outer Rim colonies have always been rather adamant about keeping out of Core Worlds politics, and the Confederation's recent movements have not made the situation any better.
Rim ships are more well-armored than their Core counterparts, and many of the larger vessels feature "lances", devastating short-range energy weapons.
While the Core and Rim have always been at odds, armed conflict was at an all-time low until recently, when a starliner carrying several Confed VIPs was attacked and destroyed near The Gap, an area filled with gravitational anomalies and no stars. A single survivor made claims of shadowy vessels, appearing suddenly and swarming the ship only to vanish just as quickly. Naval officers are quick to dismiss the story as Rim stealth ships, but the more open-minded secretly believe a more sinister threat to be lurking just out of sight...