I am currently worldbuilding for a fantasy world, and my approach for crimebusting there is simply a magically sealed off island, to which various factions and populations send of their ''bad apples'' to live out their lives on this one ''colony with no laws''. In essence, because of the available magic, it's easier for them to write these people off than sustaining them.

This made me wonder what prompted the development of modern prison system? ''Prison'' ought to be a very cultural phenomenon rather than ''natural''. Having a ''sophisticated'' society seems to be a prerequisite. I.E., if someone kills my mother, it's much more logical to decapitate them then and there, than use other peoples money to measure how many years I shall allocate to him within a specifically build building. Never mind the fact that, to regularly feed the killer and make sure he doesn't escape his assigned quarters, I'd need to employ someone. And then, oFcOuRsE, someone else, who'd manage those employees.

Obvisuly, in a modern industrialized world, there are ways of how to monetize (exploit) those sad souls. You could also (iN tHeOrY) run experiments on them under the table. Dont forget all the unemployment it would mend! (Prison guard unions being butthurt about weed not being punishable offence anymore!?) So there's a value proposition to villainize and then incarcerate as many people as necessary.

BUT what was the impulse for the leap to happen? I hope to hear some entertaining versions!