The answer to this question is 10,000 indians.
They gathered in that place because of the Treaty of Fort Laramie.
The treaty of Fort Laramie divide the lands that exist on top of united states into several parts, and determine which part of region that couldn't be claimed in any way by the Government
The homestead act freed African Americans to settle in Great Plains.
The answer for “Which ruthless emperor blames Christians for setting fire to Rome” is Nero