The Advent are a splinter interstellar branch of Humanity in Sins of the Solar Empire.
The Advent are a faction of Humans that split off from the Trade Emergency Coalition and were exiled for their ways. They would return to see the TEC at war with a mysterious ancient race known as the Vasari. During their exile, the Advent developed technologically and culturally. They became masters of a new radical technological field that became known as PsiTech. By amplifying and controlling the artificially engineered psionic powers that they developed, the Advent managed to create new and powerful as well as potent weapons to use against their enemies.
This is reflected in their starships which sacrifice endurance for specialised supporting equipment from their psionically gifted crws that are used to enhance the Advent's attacks on enemy ships or entire planetary populations. Infact, their psionic skills are so great that the Advent are capable of transfering the consciousness of entire crews and placing them in new bodies should their original bodies be destroyed.
The telepathic link to all the members of the Advent is called the Unity and seek to expand its teachings to other members of Humanity.