Cultural isolation due to geographic factors afflicts not only peoples isolated in mountains or on islands far from the nearest mainland, but also peoples isolated by deserts or in places isolated by a lack of navigable waterways -- or even by a lack of animal transport, as was the situation in the Western Hemisphere when Europeans arrived and brought horses that were unknown to the indigenous peoples.
Cultural isolation can also be due to government decisions, as when the governments of 15th century China and 17th century Japan deliberately isolated their peoples from the outside world. At that time, China was the leading nation in the world. But it lost that lead during centuries of isolation.
Sometimes isolation is due to a culture that resists learning from other cultures. The Arab Middle East was once more advanced than Europe but, while Europe learned much from the Middle East, the Arab Middle East has not translated as many books from other languages into Arabic in a thousand years as Spain alone translates into Spanish annually.
Against this background, racial and ethnic leaders around the world who promote a separate cultural "identity" are inflicting a handicap on their own people. Isolation has held back many peoples in many lands, for centuries. But such social and cultural isolation serves the interests of today's ethnic leaders.
They have every incentive to promote a breast-beating isolation. It is a sweet-tasting poison.