But 1864 saw the situation descend into full-scale war on the central plains, with violence spreading across a wide area and both American civilians and Cheyenne people dying in increasing numbers.

In June 1864, Governor Evans issued a proclamation that effectively declared open season on hostile Indians — inviting citizens to kill “hostile Indians” wherever they could be found, while specifying that friendly Indians could gather at specific points to receive protection.

The proclamation was ambiguous enough to be dangerous: the distinction between hostile and friendly was in practice determined by the soldiers doing the killing.

A month later, Evans issued a second proclamation that authorized Colorado citizens to “kill and destroy, as enemies of the country, wherever they may be found, all such hostile Indians.” Chivington used this proclamation as authority for what he was planning.