"I will show you fear in a handful of dust." -T.S. Eliot, "The Waste Land"
A recent technology shows a way of (relatively) non-invasively modifying brain. Imagine if microparticles were manufactured and covered in proteins that allow it to bypass the blood brain barrier after consuming it orally. Couple that with a hat-mounted transducer, and you'd possibly have a way to zap the pain and pleasure centers of the brain (amongst other ones). From there, Pavlovian conditioning could turn one into a nearly zombie-like servant. What could possibly go wrong?