Slavery

Historically slavery as concept in Troïka originally started with the Orcs whom sometimes forced captives to perform manual labour. This did not end up being wildly adopted. One of the big orc tribes, Bleeding Jaws, ended up heavily using slaves whilst the rest saw them as a potential liability in case of rebellion and kept there numbers low.
It didn't see heavy adoption until the Conflict against Humankind. Slowly the idea started to spread that as a punishment for there aggression it was justified to enslave the non-human agressors. Initially these slaves where used for general labour the cities needed but some merchants started getting ideas and the ability was born to buy a sentence from a city. You would offer a donation to the local municipality and in exchange you would get the honor of carrying out the punishment of one of these slaves essentially allowing you to decide what they'll do whilst taking the burden of feeding and housing them. This quickly started to be a booming business and in some cities particularly in Atzul most local criminals where sentence to work of there sentences in slavery and pawned off for a profit, leading to unjust sentencing to rake in the profits.

All of this ended with the advent of the Tragodian Emprie. Tragodia I immediately outlawed the practise calling it ignoble. Whilst at the time there was a lot of pushback the sheer political power of the Emperor was too much to stop.
In the current day slavery is still outlawed in all of Troïka. Despite this some cases of it still happen in the criminal underworld and some noble houses still participate in indentured servitude or other means to force people into working whilst technicly not being slavery.