Although most of the largest consumer countries will get access to an Xbox One, there are still a large amount of countries that Microsoft won't support, at least at launch, and there's a possibility the new console won't be available in other countries at all, or at least for a while either.
If you're located in the following countries, getting an Xbox One should be easy enough for you, as long as you can find stock:
On top of this, the Xbox One will be 'geographically locked' to the country it first resided in. This will mean that your country will not be able to be usable in any country other than the one it was used in, so if your country isn't on the list, you won't be able to ship an Xbox to your country, as the mandatory online will mean Microsoft will be able to suss out whether you're in the right country or not based on your IP address.
If you move to another country, you'll have difficulty using your Xbox One as well- Microsoft may work on adding more countries.