Complex sentence: The part of South America where the Kali'na live is very sparsely populated, however this ethnic group is such an extreme minority in all of the countries in which they are well established that locally they are a majority only in certain very secluded areas.
Split into simpler sentences: The part of South America where the Kali'na live is very sparsely populated. However, this ethnic group is such an extreme minority in all of the countries in which they are well established that locally they are a majority only in certain very secluded areas.