Until a few years ago, birth in Northern Ireland conferred citizenship in two states: the UK and Ireland.

Was this unique in modern history, or are there other similar examples?

  • I was wondering about situations like an aircraft flagged in one country flying through the airspace of another... Sep 2, 2023 at 6:44
  • 1
    en.wikipedia.org/wiki/List_of_territorial_disputes includes several regions where both claimants have jus soli citizenship. In some cases there are even three, e.g. a baby born in Sapodilla Cayes could conceivably get Belizean, Guatemalan and Honduran citizenship at birth. Bajo Nuevo Bank and Serranilla Bank are each claimed by four nations, but only three of them have jus soli (Colombia does not). Sep 2, 2023 at 6:51
  • Most of these are theoretical because the regions are uninhabited, and so most likely nobody has been born there in modern history. Sep 2, 2023 at 6:52
  • @NateEldredge usually, rules granting nationality to a child born in an airplane or on a ship of the state of registration apply only if the child would otherwise be stateless.
    – phoog
    Sep 2, 2023 at 9:56
  • "Until a few years ago, birth in Northern Ireland conferred citizenship in two states: the UK and Ireland." The UK has not had unconditional jus soli since 1983, and the Republic of Ireland has not had unconditional jus soli since 2005. Those are not "a few years ago".
    – user102008
    Sep 3, 2023 at 17:24

1 Answer 1


This would require that a country grant jus soli to an area outside its control, which often involves a territorial dispute, as Nate Eldredge's comment mentioned. Many territorial disputes are over small, often uninhabited areas, but some are not.

One territorial dispute that comes to mind is the Falkland Islands -- Argentina is jus soli, and the UK was jus soli until 1983 (and British overseas citizens were later granted full British citizenship). So someone born in the Falkland Islands in 1983 is now both a British citizen and Argentine citizen, regardless of the status of the parents, according to each country.

Another example is the territorial claims in Antarctic, of which the UK, Chilean, and Argentine claims overlap. Argentina has jus soli; Chile has jus soli except that it is not automatic for children of transient foreigners, but they may opt for Chilean citizenship; and the UK had jus soli before 1983. So someone born in the area overlapped by all 3 claims will have Argentine citizenship and can opt for Chilean citizenship (though they would likely only opt for Chilean citizenship if they were part of a Chilean family), and if born before 1983 will also have British citizenship.

It is possible that, if and when the territorial dispute is resolved, there might be some provision regarding the citizenship of people born during the dispute. Perhaps a country giving up claim on a portion of territory will retroactively invalidate the jus soli citizenship of people born in that area. Or perhaps the people will have to choose one of the two jus soli to keep. Or perhaps they will be able to keep both unless they choose to renounce one. It is up to the countries involved.

  • Have there actually been instances in history where a country revoked the citizenship of some of its own citizens as part of a treaty, when those citizens had not otherwise done anything wrong? It seems like a pretty extreme step, and maybe unconstitutional in many cases. Sep 9, 2023 at 17:08
  • @NateEldredge “their own citizens” Is rather begging the question, no? I doubt any treaty ever led to citizenship being forcibly revoked, but following the Velvet Divorce citizens had a year to opt for Czech or Slovak citizenship. I suspect that’s not an uncommon pattern, where citizens are free to choose their citizenship but may not retain both.
    – Sneftel
    Sep 9, 2023 at 17:43
  • @NateEldredge it seems as though a country giving up territory can take a few different approaches to its citizens residing there: retain citizenship no matter what, retain citizenship only if leaving the territory, and lose citizenship no , matter what. I imagine you can find examples of each fairly easily.
    – phoog
    Sep 9, 2023 at 17:52
  • @Sneftel: I mean it in the sense of "people who had been considered citizens up to that point in time". The Czech/Slovak citizenship issue is interesting. I suppose in some sense it meant that everyone had their Czechoslovakian citizenship revoked, but that was for the simple reason that Czechoslovakia ceased to exist. Sep 9, 2023 at 17:55
  • @phoog: It's the third one that I would find surprising. I'm not sure where I would look for an example. Sep 9, 2023 at 17:55

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