Conflicts between the Sioux Indians of the Plains and the US Army spanned from

Conflicts between the Sioux and the U.S. Army began in the 1860s, including the Dakota War of 1862, and continued into the 1890s, with the Wounded Knee massacre in 1890 marking a major final clash. So the best choice is “the 1860s to the 1890s.”

AI-written and checked against the verified answer.