If say for example, your mother gave birth to you on a trans-atlantic flight whilst you were over unclaimed ocean territory, to which country would you owe your allegiance? Where you took off? Where you land? Atlantis? Or do your parents decide based on their nationality? If this is the case, and THEIR nationalities are different and they can’t decide, then what?
Most countries (probably all) confer citizenship upon people born to citizens outside the country. For example, if your parents are American citizens, and you’re born on the moon, you’re automatically an American citizen too. (You may also get to be a citizen of the moon. 
)
Ireespective of where you are born, for most countries it is the nationality (born or aquired) of the parents which decides your nationality. If they are of different nationality and can’t decide then tough luck. You could decide yourself when you are an adult.
If you on a ship at sea, you are inside the jurisdiction of the nation whose flag is flying on that ship.
If you are on an aircraft, you are in the nation you are sitting in & subject to their laws, until the wheels leave the ground. Then, you are subject to the laws of the nation of origin of the aircraft.
Poorly phrased, but you get the idea.
<Ernie> I don’t want to live on the moon. </Ernie>
(Unless it’s Elmo’s lavendar moon. That would be cool.)
In this case it’s not different from being born anywhere from parents of two different nationalities. Besides, they don’t necessarily have to decide. In most places, you can keep both nationalities, even in many places which don’t recognize dual citizenship.
Aw, does this mean I can’t have kids that belong to the great nation of Rand McNally?
What if mommy is dual citizen of A and B, and daddy is dual citizen of C and D? Does little Johnny get to have quadruple citizenship? What if he get married to little Suzy in the same situation? Do the grandkids get octuple citizenship? 
That could be possible, depending on the laws of the countries A,B,C and D. But it must be quite rare, since in many countries, at least one of the parent must have been born or have lived for some duration in the country for the children to be granted citizenship. But some countries will grant you citizenship even if only your great grandmother was a citizen of said country. I believe (though not sure) that Ireland and Germany fall into this category.
But keeping up with half a dozen citizenships probably involves a lot of paperwork. It should be fun, though. I’d like to be in this situation.
Now, i’m wondering what could be the “world record” for multi-citizenship. Does anybody have an idea? I’d be really curious to know.
Trying to answer my own question, I gor several hits with “four citizenships”. The greek politician George Papandreou states in an interview that he has five citizenships (I found somewhere that besides being Greek, he was also Polish and American, though he renounced to his american citizenship when he got elected to the parliament. I’ve no clue what the two others could be), and someone on a personnal page states his mother had five, too.
“six” or “seven citizenships” didn’t return any relevant page.
I thought it was, once the plane is off the ground, you’re subject to the laws of the destination of the flight. Hence, if you’re on Air France and just took off from Paris and on the way to New York, you’re officially on U.S. territory once you’ve taken off.
D
Sure you can, but don’t let the hamburgers get them.
Do most countries automatically grant citizenship to all people born there?
Good question. Jus Solis (by the Right of the Soil) citizenship in the USA is actually quite liberal in that sense: anyone born in US soil “and subject to the jurisdiction thereof” (IOW your mother is not a diplomat with immunity or a member of an invading military) is a US citizen, even if the mother is there illegally or temporarily.
Many other countries are more restrictive as to Jus Solis citizenship(), granting it to the children of those (not themselves native) who, depending on the country, are (in increasing order of difficulty): legally in the country; not merely in-transit; on an immigrant visa rather than a work or study visa or refugee/asylee status; already official permanent residents; already naturalized citizens. Then there are the countries where naturalization is almost (or truly) impossible, and you can have multiple generations born w/o becoming eligible for native citizenship (e.g. Kuwait). IIRC most modern countries do presume Jus Solis citizenship to anyone born there to whom a different specific nationality cannot be unambiguously ascertained (e.g. foundlings).
() the counterpart of Jus solis is Jus Sanguinis, by the Right of the Blood, i.e. inherited citizenship. Virtually every nation has this, with varying terms (e.g. you can’t just keep automatically transmitting US citizenship to your descendants abroad forever, after your children, there are conditions to be met if the grandchildren want it)
Not sure about “most”, but a lot of coutries do not. My freind was born in Denmark when her mom went into labor a bit early (these days, women who are that pregnant are not encouraged to fly). My friend was not granted citizenship due to being born their because her mother had to be a Denmark citizen. There was quite some confusion about her citizenship for awhile (though she was Jewish and had Israeli citizenship) and for awhile it seemed she was practically stateless (if she hadn’t been Jewish, I wonder).
Her parents are both Canadian (and Israeli) but my friend had to be naturalized as a Canadian citizen, which she did when she was 17 or 18.
There are also people whose birth countries have disappeared. I have a friend who fled the U.S.S.R. (with her family) as a child in the mid-eighties. Her parents naturalized in the U.S., but after she turned 18, so she was not also naturalized. She had “international refugee” status for nearly a decade.
I seem to recall that this is a frequent problem for children born in refugee camps - the host country doesn’t want them, and if the refugees eventually return, their native country may not acknowledge them either. However, many war-torn countries are sufficiently disorganized that children can be slipped into the system somehow.
mischievous