The Supreme Court is once again hearing arguments on whether President Donald Trump can deny citizenship to children born to parents who are in the United States illegally or temporarily. The Wednesday case stems from an executive order Trump signed on the first day of his second term ending what’s known as birthright citizenship, which guarantees citizenship to nearly everyone born on U.S. soil. But while the concept has been part of U.S. law for well over a century, it is relatively rare around the world. Only about three dozen countries guarantee citizenship to children born on their territory. Most countries follow the principle of jus sanguinis, or “right of blood,” with a child’s citizenship based on the citizenship of their parents.