Slaves In Space And Time

During the Solar Union period of Poul Anderson's Psychotechnic future history, a small group of human beings enslaves the population of an extra-solar planet. Slavery is illegal in the Union but how can the Coordination Service know what transpires in a remote planetary system with no record of contact?

In the First Empire of the Psychotechnic History and the Terran Empire of the Technic History, slavery is legal. In the latter case, condemned criminals can be enslaved. In a remote part of the Empire, an impoverished semi-aristocratic family chooses by lot some of its members to sell into voluntary slavery. Flandry buys Ella and treats her as his mistress. When she has willingly helped him with a difficult case, he frees her, buys her enslaved kinfolk, frees them and gives them some start-up capital. Flandry cannot help living in a slave-owning society but is responsible for how he treats slaves.

Time travelers are more likely to encounter slavery than space travelers. When Manse Everard is a guest of Hiram of Tyre, he finds a slave girl in his room. He would be wrong not to use her services but treats her with respect. Later, he frees her and arranges a suitable marriage. We commend Flandry and Everard.

In SM Stirling's Against The Tide Of Time, the King of Babylon generously gives the Nantucketers two hundred palace slaves. (See the unanswered question here.) Slavery, doing a Walker, is a serious offense in the Republic. However, to free these slaves would insult the king and endanger them. But the Nantucketers do:

tell the slaves that they are in fact free;
also tell them that they work to eat - but they already know that;
start paying some of them a small amount to do useful work;
teach them language and literacy.