Outside of the Americas, most countries follow the legal principle of jus sanguinis, or “right of blood,” with a child’s citizenship inherited from its parents, no matter the place of birth.
In the European Union, for example, no member states grant automatic, unconditional citizenship to children born to foreigners.
But American legal practice is descended in many ways from English common law, which had long provided for citizenship based on a child’s place of birth, the legal concept of jus soli, or “right of soil.”
The UK, though, abandoned jus soli with the British Nationality Act of 1981.
Under the new rules, people born in the UK get citizenship only if at least one parent is a British citizen or has “settled status” under the law.