The vanishing of languages, like those of living species, is an event that has been repeated many times in history. Localized disasters such as a volcano eruptions, great floods or warfare have played a part, but in the modern era the spread of Europeans--and European diseases--has greatly accelerated the pace of destruction. Local or regional language communities may be overpowered by a dominant metropolitan language, which increases the pressure to neglect the ancestral tongue in favor of the new one and is seen as the key to prospering in the dominant culture. Children may be forbidden to use their mother tongue in the classroom, as has occurred to many groups, including the Welsh, Native Americans and Aboriginal Australians. Speakers of minority languages have been forcibly relocatedand combined with speakers of other languages, as happened when Africans were brought to the Americas as slaves. Practices such as these have made Native American languages the most imperiled of any on the earth. The death of a language is not only a tragedy for those directly involved but also an irretrievable cultural loss for the rest of the world. Through language, each culture expresses a unique worldview. Thus, any effort to preserve linguistic variety implies a deep respect for the positive values of other cultures.