Hokay, so here's the driving idea behind the campaign map:
Follow the cannon StarWars timeline, later we can go back and do the prequel, later we can release an expansion.
Make the player play both sides of the story, but how do we pick? We make them play the winning side of each campaign.
How is the plot flow managed? In the StarWars universe, there's a lot of events that happen around the same time, but all happen before something else.
For example:
Campaign A unlocks: B,C,D
B+C unlock E
D + E unlock F
I'll draw out an example chart, but basically, the Empire and Rebellion have a lot more going on than is in the movies. Even 'TIE Fighter' went and helped quell a civil war. We can structure the campaigns like this so that the player has a lot of choice in how they play through, except that they'll always end up with the same ending/Blowing up DS2. (Or we can continue on)