Sometime towards the end of the 15th century, the French word passeport (from passer, ‘to pass’, and either port, ‘harbor, or porte, ‘city gate’) was adopted by the embryonic hybrid language that would eventually become English and simplified into ‘passport’. Today, this unassuming two-syllable word is the fulcrum on which much of global politics turns.

Modern passport laws have been in place in the West since the 1500s, but the emergence of long-distance railway systems in the 19th century made them all but impossible to enforce, and there were generally few barriers to international travel until World War I. Borders were still being defined and disputed; as such, they were only loosely patrolled.