The sheep wars, or the sheep and cattle wars, were a series of armed conflicts in the Western United States fought between sheepmen and cattlemen over grazing rights. Sheep wars occurred in many western states, though they were most common in Texas, Arizona, and the border region of Wyoming and Colorado. Generally, the cattlemen saw the sheepherders as invaders who destroyed the public grazing lands, which they had to share on a first-come, first-served basis. Between 1870 and 1920, approximately 120 engagements occurred in eight states or territories. At least 54 men were killed and some 50,000 to over 100,000 sheep were slaughtered.

In the Western United States and Canada, open range is rangeland where cattle roam freely regardless of land ownership. Where there are "open range" laws, those wanting to keep animals off their property must erect a fence to keep animals out; this applies to public roads as well. Land in open range that is designated as part of a "herd district" reverses liabilities, requiring an animal's owner to fence it in or otherwise keep it on the person's own property. Most eastern states and jurisdictions in Canada require owners to fence in or herd their livestock.