The system of passports as we know it today dates from roughly a hundred years ago, when leading world powers were trying to figure out a way to regulate international travel in the messy aftermath of World War One. Ever since, these documents have been seen both as boarding passes to freedom and as levers for government control. But which of the world's passports open up the widest vistas of international travel? The Henley Passport Index has an answer. For 199 passports, it tallies up the number of countries that are accessible without obtaining a prior visa. Here's a map of which countries' passports are the most powerful right now.