求翻译：19世纪60年代，大平原上南北移动的野牛群仍然非常稠密.在内战后的西部开拓中,白人移居者对野牛进行了野蛮的屠杀,致使野牛灭绝.与此同时,白人拓居者在美国政府的支持下推行种族灭绝政策,导致失去生活所依的印第安人陷入了严重的生存危机,这种残暴和不义之举是无可挽回的历史失误.使美国人反思这段历史.，并铸造镍币来纪念这段历史。是什么意思？

In the 1860 of the 19th century, large plain Shang North-South mobile of wild cattle still very dense. zainei post-war of Western open up in the, white moved to who on bison for has savage of massacre, cause bison extinction. Meanwhile, white extension UN-Habitat who in United States Government of s

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The 19th century 60's, in the great plains the north and south migration reactionary group extremely was still dense. Develops after the civil war west, the Caucasian transplant has carried on the barbaric slaughter to the reactionary, causes the reactionary to exterminate. At the same time, the Cau

In the 1860 of the 19th century, large plain Shang North-South mobile of wild cattle still very dense. zainei post-war of Western open up in the, white moved to who on bison for has savage of massacre, cause bison extinction. Meanwhile, white extension UN-Habitat who in United States Government of s