Alien Slaves
In a harsher world with regressive moral views, or fundamentalist religious views, combined with a sanctity of human life, it may be easier to adbuct aliens from Tau Ceti E to work as slaves in our star system, man ships etc
Human slaves would be morally abhorrent, but those more inclined to morality based on what's socially acceptable would not wince at non-human slaves, in the same way many people enslave bears to dance, or when faced with a sentient AI would think of it as nothing more than a toaster
Make their reproductive cycle involve things only found on Tau Ceti E, or things that are impractical to move ( e.g the female equivalent or queen bee of the species is 30m tall and weighs several hundred tonnes )
Examples/Precedents
A common scifi trope
The Ood
An example of such a species in current Scifi would be the Ood from Dr Who, who have a giant primary life form that's trapped and kept under control in order to repress the Ood
The Ood, also known as Oodkind, were a gestalt species of telepathic humanoids native to the Ood Sphere. Humanity enslaved the Ood, mutilating them to ensure a dedication to servitude.
The Ood were a peaceful herd-race originally. In the 39th century, humanity discovered the Ood, enslaved them, and used them to perform menial tasks throughout the three galaxies of the Second Great and Bountiful Human Empire. The external hindbrain of the Ood was extracted by Ood Operations and replaced with their translator globes. With their connection to the Ood Brain severed, they followed the orders of humans. Ood Operations kept this procedure a secret from the rest of humanity, spreading the belief that the Ood were naturally servile and offered themselves for servitude. (TV: Planet of the Ood)
Goa'uld
A parasitic life form that stole technology and had a restricted number of hosts chanced upon Earth and enslaved the population, farming humans for new bodies to act as hosts
Ironically, the reverse became true in the show when a human civilization chanced upon a Goa'uld queen and farmed her for chemicals. Here is a Goa'uld queen:
That wasn't enough it seems, a new sub-species was genetically engineered for slavery as soldiers and incubators, the Jaffa
Helots
A real life example from Antiquity, the Helots, slaves of the Spartans
The Helots, slaves/serfs of the Spartans, who outnumbered the Spartan citizenry by so much that the Spartans had a tradition of hunting them down and killing them. This wasn't considered murder; one of the duties of the ephors (Spartan magistrates) was to declare war on the helots every year so that Spartan citizens could legally kill them (the fact that they were surrounded and vastly outnumbered by slaves who had every reason to hate them is believed by some to account for the Spartans' extreme militaristic badassery). The people from Sparta certainly considered themselves to be a breed apart. To the point that, in order to be a Spartan soldier, you had to be able to trace your origins back several generations of pure-blooded Spartans. This... did not work out so well for them, as being so incredibly exclusive in who can be a "soldier" tends to result in running out of trained soldiers. Not all wars are fought in very narrow mountain passes where numbers don't matter.
I could go on, there are many examples from scifi, and many examples of colonial imperial powers in history who've treated continents the same way ( Arab traders in Africa, British Empire, Colonial France, Confederate USA ). If you need inspiration for a slave nation, look the the dominion of Draka series of books by Stirling