You could just move to another country and you'd be subject to their law. And that's probably because the idea of nationalism became important in the 18th centu

You could just move to another country and you'd be subject to their law. And that's probably because the idea of nationalism became important in the 18th century. Sure there are universal human rights, but that's still new and many countries don't honor them: minorities are often denied basic human rights, some countries still have the death penalty, etc.