Well if it is military based, I would do a rough outline of the major factions. Who is fighting who, and why?
Next I would define the minor factions. The arms dealers, mercenaries, supply routes, and faction turncoats/spies.
Then I would define the internal bureaucracies that are leaching off these factions.
This will give you a well-defined feel for the setting.
Then I would make 1 or 2 major characters that are going to symbolize each of the factions. No stats, just story, about 100 words each.
Now you will have characters that will give the background a life of it's own. These steps will give you a functional setting in which to insert your adventure hooks. Each character you write can come with it's own set of adventures as well.
Next make the characters write their backgrounds. Have them answer the basic questions:
When was your character born?
What did your character do for a living?
What were your character's hobbies and interests?
What was your character's relationship with his or her family like?
What languages does your character speak?
Any special skills?
What is your character's wealth level or social status?
Who are your character's friends and enemies?
What is your character's morale code?
What are the most important moments of your character's life?
What are your character's plans for the future?
After they answer these questions, let them stat their PCs. These questions will give each character a "built-in" adventure that you should easily be able to weave into your previously defined factions and characters.
If you PM your email to me, I will add you to one of my game sites so you can see this process in action (and feel free to plagiarize as you wish).
Hope this is helpful.