I think there is a misunderstanding of what constitutes a market here.
The idea of geography defining a market broke down in the 1840s, when the train become common. The telephone eroded it further in 1875 and the car really put the final nail in its coffin in the 1920s. Thinking geographically is about a century out of date.
It can still apply, but only when the reach of an organisation is limited by local distribution and marketing. For example if you use your own vans coming out of a central depot, rather than using an international courier company. Or if your only means of publicity is through the local newspaper. Or you still use the antiquated customer acquisition methods of a man who has to visit people just to make a sale (sounds ludicrous now, doesn't it).
Such limitations, these days, are self-imposed - there is no need to restrict yourself in this way. Nor is there a need to accept limitations placed on you by language, by media (which still often think geographically) or taxation.
Markets these days are more accurately defined by who would be interested. Teenage boys, for example share a lot of the same interests globally. It is easier to create packaging in multiple languages than repitch the same product to, say, teenage girls.
Markets are also defined by the means to create awareness. If you use, for example, Pinterest, you appeal to a global audience - only having your product available in some of the territories is quite simply wasting the interest you generate (and thus the funds to do so).
For startups, this has another risk. If you launch in one territory, you run the risk of getting feedback stats which only apply there. You can create a product which you think has wide appeal, but is actually only designed for that one niche market.