The LF was a group of exiles sent out into the galaxy by SA because they were murderers. The SA didn’t know there were other species in the galaxy so they gave them 2 destroyers, The Eva & Lucifer. The LF enjoyed killing which is why they slaughtered the ancients. The LF had modified their supplies, which would last for 20,000 Years to form Shivan Super Laser, an Impervious Shield system and other weapons, which they mounted on their destroyers After the Ancients were destroyed the LF were bored for 8000 years and decided to launch all their weapons at the GTA and PVN, but the LF was destroyed and eventually eliminated completely.
32 years later a Racsh… Racshas… Shivan cruiser entered GTVA space and was immediately fired upon by the Terran cruiser. (I know the Command Briefing video contradicts this and shows the Shivan cruiser firing first, but it was unlikely to be actual footage of the battle because a massacre was implied) The SA wasn’t happy about the unprovoked murder of 5000 Shivans and immediately thought of the GTVA as an enemy. A few months later the SA captured Aken Bosch but, for the purposes of this discussion their communication was extremely crude. The SA didn’t understand Bosch but their ships were still being destroyed so they sent in a Sathanas to stop the attacks on their ships. Unfortunately it was destroyed, the Shivans were extremely angry at the Murder of 30,000 Shivans so they decided to send in a small portion of their fleet (80 Sathanes) to eliminate the GTVA entirely. At this time they managed to speak to and understand Bosch , Bosch told them about the LF and why we attacked them. The Shivans held an emergency meeting and decided that instead of wasting valuable resources going through all of their systems back to their homeworld where their fleet was. So they decided that, instead of wasting all of that energy they would use the Capella star as a Slingshot to get back to their Homeworld, in the process creating a nebula for the GTVA to take energy from as a peace offering.
Q. Why were the GTVA ships attacked as they were evacuating Capella?
A. The attackers were rebels and relatives of Shivans killed during the war
Q. Why was the Bastion attacked?
A. The attackers were rebels and relatives of Shivans killed during the war
Q. What happened to Bosch
A. He was on one of the Cain class cruisers on the way to Vega, but was destroyed.
Flames welcome

EDIT: Q. Anything else
A. Its because they're aliens
