Final answer:
Red Cloud's War began because the US government built a railroad through Sioux hunting grounds, which violated previous treaties and disrupted the Sioux's way of life.
Step-by-step explanation:
Red Cloud's War began because the US government built a railroad through Sioux hunting grounds. This angered the Sioux as it disrupted their way of life and violated previous treaties. The Sioux tribes, led by Chief Red Cloud, fought back against the US government's encroachment on their lands and resources.
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