Even nowadays, birthright citizenship jus soli is far from universal. Jus sanguinis was much commoner in old times and is far from dead. You belong to a family, to a clan, to a country by that connection. There are countries where people who have three generations born there are not citizens because of not having four. . . and lawyers who track down distant blood connections to claim obscure citizenship on behalf of American criminals on Death Row. (Didn't we fight a war over that once?) Ancient Greek accounts are full of tales about how some group or other, like the helots, was subjugated on account of some long-ago historical origin or offence.
Not to mention that if your father's was matrilineal, and your mother's patrilineal, you could be out in cold. That was fairly rare, but Athens, for instance, required that both parents be citizens or, at most, that the mother be a citizen of selected other cities, under treaties.
Even jus soli had its complications. In England, you had a right to relief in the town in which you were born. (Or one where you had rightfully resided for a year and a day, which is why servants were hired for a term of one year.) As a consequence, there were laws about giving refuge to pregnant women, especially since a woman who needed help was particularly likely to be poor, and their treatment could be brutal. (Some towns shifted it to the town in which you had been conceived, so you could fall between the cracks that way.) New England had followed that for a time and then switched over to the children of legal residents -- and to avoid granting residence to laborers "warned them out" when their labor was not needed. They didn't actually force them to move, just ensured that a year and a day would not make them residents. Then they would try to figure out where their orphaned children should be dumped. There was one case where three children under ten were shuttled about in midwinter as towns refused their charge.
That's one complication you seldom see for characters.