I was reading an article about the Sentinelese, an uncontacted culture living on North Sentinel Island in the Andaman Island chain. There are dozens of uncontacted tribes, mostly in Papua New Guinea and the Amazon. How do historians work around the inherent lack of communication to learn about the indigenous peoples that shun outside contact? How has this changed from the past when expanding cultures/empires encountered people who wanted no contact? I'm aware that many instances were either conquest or extermination such as what was seen in the 16th-19th centuries, but are there historical precedents of cultures intentionally leaving another group to their own devices?
While the media likes the image of uncontacted peoples, very few of these groups are truly isolated (the Sentinelese being an exception).
That said, this is really more a domain of anthropology and so you would get a better response from /r/askanthropology.
Usually historians in such an instance would resort to more anthropological methods to study these cultures. The nice thing about history is that it is very flexible in its methodology. In fact, many of the recent innovations in history have incorporated anthropology into its methodologies. Since history is basically just a study of change over time, there is essentially no limit to the kinds of evidence one can use. One can use anthropology, science, sociology, political science, economics, etc. to make historical arguments. As long as the argument is sophisticated, uses an eclectic and diverse arrangement of sources, then it will be a good argument, which will make it a good history.