The Grattan massacre, also referred to as the Grattan Fight, was the initial conflict of the First Sioux War, occurring on August 19, 1854, between the United States Army and the Lakota Sioux warriors. This event took place east of Fort Laramie, located in the Nebraska Territory, which is now part of Goshen County, Wyoming.
A small contingent of soldiers entered a large Sioux camp to apprehend an individual accused of killing a settler's cow, despite the fact that such issues were supposed to be resolved by the US Indian agent according to treaty agreements. After one of the soldiers fatally shot Chief Matȟó Wayúhi (Conquering Bear), the Sichangu Lakotas returned fire, resulting in the deaths of 29 soldiers, including Lieutenant John Grattan and a civilian interpreter.