Question

conflicts between the sioux indians of the plains and the us army spanned from the 1820s to the 1850s. the 1860s to the 1890s. the 1870s to the 1900s. the 1880s to the 1910s.

Explanation:

The conflicts between the Sioux Indians of the Plains and the US Army were prominent from the 1860s - 1890s, marked by events like the Great Sioux War of 1876 - 1877.

Answer:

the 1860s to the 1890s.