Slavery

A slave was an individual forced to perform tasks. It differed from  a free servant, who could quit.

Many species, such as the Ood (DW: Planet of the Ood) and Mutos, were forced into slave labour. (DW: Genesis of the Daleks)

The Huducts enslaved the Anubians by using mind-controlling torcs. After the Anubians were liberated by K9 Mark I, the Anubians turned on their former masters and enslaved them in the same way, even though K9 intended for them to reconcile in peace. The Anubians later developed space travel and enslaved other species. (K9TV: Curse of Anubis)

The Sycorax practised slavery. During their invasion of Earth on Christmas Day, 2006, they planned to sell half of humanity into slavery. (DW: The Christmas Invasion)

In the 21st century, there was a black market in alien slaves on Earth. John Harrison purchased a group of Skullion slaves on this market. (SJA: The Man Who Never Was)

Some races, such as the Daleks, altered individuals into becoming slaves. Example of such are the Robomen, (DW: The Dalek Invasion of Earth) Cybershades (DW: The Next Doctor) and New Humans. (DW: New Earth)

Humans have regularly been subjugated in slavery. Examples of this are their forced labour in Bedfordshire, (DW: The Dalek Invasion of Earth) the building of the New Time Lord Empire (DW: Last of the Time Lords) and forced experimentation by the Daleks. (DW: Daleks in Manhattan) Humans have often enslaved other members of their race. (DW: The Romans, SJA: The Man Who Never Was)