You have the Jardaan,a faction of the original race of the Angara, who noticed that their home planet will no longer sustain them. Seeing no viable option, they create the Remnant and vaults to terraform other planets. As we see, there are many more vaults. Once enough vaults come online, it creates a distortion with dark matter, which gives rise to the Scourge. They adapt the Remnant bots to begin attacking the Scourge, which leads to the Remnant fighters, but it's all for naught. I'm thinking of the Scourge as being a corrective universal force, and the Jardaan, or rather Angaran, are trying to punch the wind here. This is when the original Angara split into two factions; the Kett and the Jardaan. The Kett is the group (much like the Roekaar) that is uneasy and not willing to fight a seemingly loosing battle. The Jardaan stay and try to fight. This is when we'd see warring between the factions. With the Kett probably having spies amongst the Jardaan, they catch wind of genetic modification. The Kett manage to steal the plans or some of the serum and begin experimenting with it after escaping the cluster. That's when they discover they can start assimilating other less advanced races. This starts turning them into beings that all look the same, have the same genetic makeup, and have a cult mentality. Meanwhile, the Jaradaan test the serum, see how crazed it makes their test subjects and scrap that plan. They refocus their efforts on creating a race that can live in the scourge while still maintaining key genetic markers that resemble the Angara. And now we have the "manufactured" Angara as we know them in Andromeda. The Jardaan are still in "Oh * mode".
Just to point out but nothing says the Jaardan are native to Andromeda. In point of fact the game alludes to the Jaardan only appearing in the Andromeda system in the last 600 years, between the initiative departure and arrival at the cluster.
One of the ways you can colonize a system is to bio-engineer your species to a new habitat. With the Angara "memories" of "re-incarnation", and the ability to interact with technology using bio-electrics it points to them being essentially a "housing" for Jaardan consciousness which are potentialy stored digitally. We already know the data they can store in a small area is immense (peebee > Eos Vault), so its feesibly they could store a consciousness of an individual.
This to me seems extremely likely as it would make the 3 main protagonists non-native to Andromeda (Initiative / Kett / Jaardan). That then allows for the possibility of a "native" andromeda species as being the Jaardans "enemy".
If one assumes the above, it then makes sense that a native species would see Jaardan as invaders, intent on altering the cluster to their criteria at the expense of a previously un-named native race. Since the Jaardan rely so heavily on tech, the scourge becomes a universal weapon against them doing so.
But there is one major bug-bear I have with the games plot.
Dark Energy. How can "dark energry" interact with matter? My physics is a bit shoddy but afaik the whole point of it being called "dark" energy is that it does not interact with matter.
