Isolation of many different groups within one country, each knowing only their own language, occurs particularly in countries where there are many different indigenous populations which are cut off from each other and from outside influences so that their language is unknown to others. Since most of these languages are unwritten it is difficult for the society at large to have any knowledge of them unless there is extensive contact with the tribe in question. Diverse unilingualism is a severe obstacle to the education of indigenous populations and their integration into national society.