They are > https://en.wikipedia.org/wiki/Energy_slave

Most wars have (often hidden) rational objectives. Even US Senator Lindsey Graham now openly admits it. "Ukraine is "gold mine" with $12 trillion of minerals West "can't afford to lose". https://www.youtube.com/watch?v=3TRPk3N8FyQ

Slavery was an extremely rational conversion of scarce bio-based energy into power. Far more effective than if used on horses or oxen. Débeir, Deléage and Hémery point this out in their book In the Servitude of Power: Energy and Civilization Through the Ages.

Because this thermodynamic conversion rationale is universal so is slavery in its many guises. Every colour and creed of humans have, all across the globe somewhere in history, been subjected to it. Because it simply made sense.

Only with the dawn of the fossil fuel era did that rationale die out and with it the logic driving slavery. Forget morals, they always come after the fact to reconstruct the new narrative. May all those demanding degrowth and the rapid transition towards a fully bio-based economy understand what certainly is awaiting them there.