The Johnson County War, also known as the War on Powder River and the Wyoming Range War, was a range conflict that took place in Johnson County, Wyoming from 1889 to 1893. The conflict began when cattle companies started ruthlessly persecuting alleged rustlers in the area, many of whom were settlers who competed with them for livestock, land and water rights. As violence swelled between the large established ranchers and the smaller settlers in the state, it culminated in the Powder River Country, when the former hired gunmen who invaded the county. The gunmen's initial incursion in the territory alerted the small farmers and ranchers, as well as the state lawmen, and they formed a posse of 200 men that led to a grueling standoff which ended when the United States Cavalry on the orders of President Benjamin Harrison relieved the two forces, although further fighting persisted.

A range war, also known as range conflict or cattle war, is a type of usually violent conflict, most commonly in the 19th and early 20th centuries in the American West. The subject of these conflicts was control of "open range", or range land freely used for cattle grazing, or conflicting sheep pasture, which gave these conflicts its name. Typically they were disputes over water rights, grazing rights, or cattle ownership.