The Mutation Wars was a highly destructive war that led to billions and billions dead.
Before the war began, a Crogenitor named Xylan created E-DNA, which allowed unnatural evolution to occur that caused evolution in mere hours or even minutes. The rest of the Crogenitor race believed it to be unstable, but Xylan refused to end his research on E-DNA.
Eventually he was banished for his actions, which had resulted in the deaths of numerous scientists during trials for E-DNA. Xylan with the help of like minded Crogenitors, faked Xylan's death by causing his lab ship to malfunction and explode. With their support, Xylan began to infect creatures and sentients with E-DNA.
These infected beings became something known as The Darkspore, and hive-minder race of viruses that planned to infect the entire universe. When the Crogenitors learn of this, the began a massive campaign to eliminate The Darkspore and the twisted Xylan, beginning the Mutation Wars. Despite the efforts of the Crogenitors, the war became more like galactic quarantine then a war between sentients.
World after world fell to The Darkspore, adding new troops to The Darkspore horde. In the end, the Crogenitor Empire fell, resulting in a victory for The Darkspore and Xylan, now known as The Corruptor. The Crogenitors, however a slim backup plan, they would send 7 Crogenitors in cryoships to the far reaches of the galaxy, saving the Crogenitor race from complete an extinction in the hopes to one day defeat The Darkspore menace.