In a world where people are more mobile than ever, nations are struggling to recalibrate who can be a citizen.

Unrestricted birthright citizenship is increasingly rare, and with only a few exceptions, it persists only in countries with negative or near-zero rates of

President Trump’s order curtailing birthright citizenship faces lawsuits over the 14th Amendment. This may be prelude to other efforts to end it.

More than 30 countries grant unrestricted birthright citizenship based on the ‘jus soli’ principle – and nearly all of them are in the Western Hemisphere. The reason is more complicated than you might think.