The Broken Tower by Kelly Braffet
Once there was a wealthy lord whose family ruled a land flowing with natural power. Each person who lived in the lord’s kingdom could access the power, which made their lives easier in a thousand small ways. One day, it occurred to the powerful man, who was called Lord Martin, that a thousand people with a little power each might well be a match for one man with a lot of power, and this idea terrified him. So he called the smartest men he knew to his great House in the city of Highfall, set them to work in a tower, and ordered them to find a way to bind the power so it couldn’t be used against him. In this, they were successful: they bound the power, but they destroyed themselves (and part of their workroom) along with it. After that, the land became a sad, grim place. Lord Martin was soon called Mad Martin, because he could never rest easily, but he and his heirs ruled for many generations.