Why vaccine passports are causing chaos

MANY COUNTRIES did not require passports before the first world war. But as the conflict spread, states scrambled to introduce travel documents to help secure their borders. The result, after the armistice, was a bewildering smorgasbord of different information for different nationalities that could create chaos rather than clarity at border crossings. But returning to a world where people could travel freely across borders was by then unimaginable.