Alliance are a serie of different mods. On the Star Wars GC, you can play the civil war Empire vs Rebel era + Black Sun and soon the Republic and CIS.
Now you can disband a fleet or a ground batallion. With only put them at orbit from one planet, you will see a additional option for to build. When you make it, the fleet or the batallion is divided at all its units. It will run with all the sides.
It can be very useful if you need troops or starships for protect many planets and you have not enough time for build them.