generational citizenship is of feudal origins put in place by a sovereign king. it is statute law, not natural law.
It’s a potential extenuating circumstance for those born of naturalized immigrant parents or even grandparents, who would otherwise have no doubt regarding their natural born citizenship status. The vast majority of such nations require a descendant of their citizens to claim citizenship themselves upon reaching the age of majority. It’s not a condition existing at birth. England was an exception at the time of Obama’s birth. They claimed the children of their citizens as citizens also, regardless of where they were born.