Okay, found Eishtmo's Capella BBQ theory--
Alright, here's the brief version of the infamous Capella Barbeque theory:
The Shivans are party animals, the greatest party animals of all time. Long ago, around the time of the Ancients, they ran out of beer. So, they took their ships and tried to get some from the Ancients. The Ancients were snoody and refused to share, so the Shivans killed them and took their beer.
Flash to FS1, and the Shivans are running low on booze once again. So they send their beer collector (Lucifer) to get more. However, the problems with the Ancients were still on their mind, so they attacked the GTA/PVN to get their beer. They destroyed Vasuda Prime when they discovered the Vasudans had no beer. However, they did discover that Earth did have beer, lots of beer. And beer nuts, very rare in the universe. Well, we all know what happened after they tried that. Anyways, the Shivans managed to find another supply somewhere else and left our friends alone.
Flash to FS2. Bosch, after studing GTI records discovers the Shivan's true reasons and decides he wants to "get down with the masters." So he opens the Knossos so he can contact them and join the party. The Shivans, still smarting from their failed attempt to get beer nuts (which as I said are very rare) sent one of their great party wagons (Sathanas) to get some. Of course, the GTVA wasn't too thrilled with Shivans moving a big ship through their space, so they attacked it.
Now the important part. Bosch finally makes contact with the Shivans and they happily let him join. Unfortuantly, some of the Shivans have a bit too much to drink and kill the Iceni crew. Oh well. Anyways, to celebrate their new-found partyers, the Shivans send their party wagons with an ample supply of meats and veggies to Capella to grill them good, using a supernova no less. Of course, the GTVA panics and seals the node. A real shame too, the Shivans were going to invite the Alliance to join them. More for them I guess.
And that, my friends, is the Capella Barbeque theory.