The Capellan world of Sirius was briefly part of the Tikonov Free Republic before that nascent state was annexed by the Federated Commonwealth. With the dissolution of the Near Earth Defense Association, Count Wrigley had to welcome his new F-C masters in order to spare his world from a protracted and ultimately doomed resistance. His wayward son, Sir Wrigley, returned to form a resistance movement against the F-C oppressors, only to mysteriously disappear three months later. Jinx and Roy Fowlker, along with several other Blowfish who came along, all went missing with Sir Wrigley.
On Altair, Duchess Selena Kyle continues to rebuild both the world and the Altair Defense Force after the climatic battles with the Skye Rangers and Comstar. Needing the Blowfish Mechs, Duchess Kyle bought out the Blowfish and reformed them into the 1st Altairan Guards. Clyde Brown, Mr O, and Katherine Pryde left with their shares to form a new mercenary company.
The other main Blowfish settled into the new organization. Izzy Finch heads research and development at the Altairan Royal Research Center, Shaniqua Johnson commands the palace guards and Roger Isa commandant of the Altairan Military Academy.
The year is 3034. The Fourth Succession War has been over for four years, leaving the Inner Sphere much changed. Half of the Capellan Confederation was conquered by the Federated Suns. The Free Worlds League suffered through a civil war. The Draconis Combine is about to lose one of its Military Districts to the new Free Rasalhague Republic. Only the Federated Suns and Lyran Commonwealth stand strong, having joined into the Federated Commonwealth super-state which controls half of the Inner Sphere.
It's a dangerous time for Altair, at the exposed corner of the Draconis Combine, it will certainly be one of the first worlds attacked when the Federated Commonwealth finally invades, and invade it will. It's only a matter of time.
Altair has a need for warriors. The player characters are such people. Whether they are Altairan natives and recent graduates of the Altairan Military Academy or a grizzled veteran looking for a stable job, Altair wants them. Good pay, high danger, lots of fun -- what more can you ask for?
My fourth campaign will be GURPS BattleTech. We will use BattleTech for Mech combat and GURPS for character details and out of Mech action. The reason I want to do this now is that GURPS 4E is due to come out and it's a good excuse to finally run a GURPS campaign. BattleTech is chosen because it's a simple universe and most sessions will be hot Mech on Mech action.