Story - Terrans
After the battle of Pollux IV, the Terran Alliance was prisoned in the Terran Containment Zone. This zone consists of the solar system and reaches to the Oort cloud. Because you can't jump through the cloud and there are just a few safe known routes through it, it's easy to keep the Terrans in there.
The Terrans have colonized most planets and moons in the solar system (where this was possible). There are several space bases in the orbit of there planets.
On earth itself, there are many large domed cities. In the biggest of them (New York City) live about 50 billion people. Most Terrans stay their whole life in the cities, and never go outside. These cities are completely self-subsistent.
Terran Allied Forces (TAF)
After the battle of Pollux IV, the few remaining forces of the Terrans were prisoned in the Terran Containment Zone. They were regrouped and formed the Terran Allied Forces.
The main mission of the TAF is to protect Earth. Because there are no other enemies in the Terran Containment Zone, the SpaceGuards are the direct opponent for the TAF.
The Terran technology is not as advanced as the Spacer's. So, Terran ships are a bit slower, have less shields and so on. Because the Terrans have limited ressources, they build any craft as compact as possible, resulting in blocky stuctures.
Later in the main campaign, you will will fly for the TAF. You have to protect Earth will all forces, that are available. You will also be involved, when the Terrans break through the Terran Containment Zone since centuries.
You will fly in several battles for the TAF. When you are good, you will make your career in this organisation also. (An uniform of an Admiral with many medals is shown on the left.)