Have you ever wondered if there is more story behind the factions/characters/enemies than it says on here? Well tell me about it! Here is what I think:
Civil Security: They are the Survivors of the Earth and are protecting any other human life left alive. They tried to create Androids to aid them in their objectives, But they malfunctioned or something and they started attacking them.
Androids: Explained above
Usurpation: They attacked the Humans and took over some of their bases. They fought and fought wiht the Civilian Security forces and you came while it was partially dormant.
What are your thoughts?