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.
In the incoming new upgrade, there are some additions, new changes in the space maps, new random reinforces, the Awacs ships control the reinforces, if you destroy them in the begining or you lose them, the starbase will not receive reinforces probably.
These modifications from Warb_Null or Evillejedi models are only some of them, there are more, each faction have different type of these units.