Funnily enough, the need to have a passport to leave your country is a relatively recent thing. Pre-World War I, people could just pack and go to another country, and passports were rarely enforced. They were more a helping document while traveling than a controling tool.

Only after WWI one of the explicit objetives of the passports was to limit the emigration of skilled people. Not to menction that most countries in America were happily receiving huge amounts of people from everywhere without too much hassle. I don't think that is happening today.