The main hurdle is language. An American working on Japanese History would have to be able to read Japanese documents, in order to research primary sources effectively. Without the language the American would only be able to access Japanese secondary sources, in translation, which cause their own problems, or secondary English language sources, which would mean that their work could essentially only be synopses or syntheses of existing work. In my own case, I specialised in French History, the Revolution in particular, so had to learn French, and 18th Century French, and then learn to read handwritten documents, using poor quality ink on poor quality paper, written by quill pens, which was quite a challenge, if rewarding.

I find it can actually be helpful to study a period or culture different from your own because it can allow you to take a farther step back and attempt to be impartial. I find this specifically helpful when it comes to time period. I like studying things like the black death, which could be insanely depressing, but knowing it happened centuries ago helps keep me detached. I'm fascinated by the reaction and historical explanations people try to use to justify "why bad things happen" and even more "why I did bad things". It is way easier to detach myself when studying the black death versus trying to study the holocaust or other 20th century atrocities and calamities. Similarly I find it more difficult when I'm studying American atrocities because they piss me off more because it becomes personal.

The biggest hurdle would be language, if you cannot understand the text, you will have issues. While translations work, things do get lost in them.

Access to documentation is another one, yes, records are getting digitized more and more, so you really don't have to go to X country to look through their records as much anymore, but it helps. It helps also in other ways, like networking and resources.