Ancient-Shivan War (FS1)
This war fought between Ancient and Shivan forces, ended with the extinction of the Ancients nearly 8,000 years before the main FreeSpace continuity. It's worth noting that the name used to define the war cannot be found in any canon sources—it's the name the community has given to the war, in light of the principal combatants (and probably because of the similarity to Terran-Vasudan War).
Details of the war are unknown. We know from the cutscenes that the Ancients were a glorious race that had been expanding its empire for thousands of years, subduing or eliminating lesser races, remaining undefeated on the battlefield. At some point, they discovered subspace, that allowed them to expand their empire even further.
Then they encountered the Shivans. The cutscenes imply that whatever Shivan force they were engaging was resistant to their weaponry, but it's not explicitly stated that the same SD Lucifer that will bombard Vasuda Prime during the Great War took part in this conflict as well. It is known that the Ancients were driven back to their homeworld. They had observed beforehand that the Shivans were not interested in planetary resources or gaining territory, sparking some hope that they would be safe on the surface. The Shivans, however, bombarded the Ancients' homeworld.
The remainder of the Ancient Empire continued to fight the Shivans desperately, and found a weakness in the Destroyers' defenses: Their shields did not operate in subspace. Tragically for them, they had no means to carry out such an attack, and were eventually eliminated.
The Ancients recorded their findings on scriptures, which will be found by a group of Vasudan refugees on Altair IV. Terran and Vasudan xenolinguists managed to decode the Ancient artifacts just in time to mount an attack on the SD Lucifer while it was in subspace, en route to Sol.