During the Civil War years the concept of breeding horses specifically for the United States Cavalry began to develope as the necessity became evident after an estimated 1.5 million horses died in the conflict, including wild horses.
After the Civil War westward migrations sparked the Plains Indian Wars. Native tribes that engaged these conflicts rode horses commonly known as “Mustangs.”
“Mustangs” developed from the Spanish and European horses that had gone wild during the colonial period (that possibly bred with indigenous stock, current research still questions if horses went extinct on the North American continent). These horses evolved into sure footed fast “ponies” which the plains Indians learned to maneuver very efficiently to fight on horseback. Their speed and agility, proved to be a most valuable asset against the U.S. Army.
Horses with lineage back to the Civil War and the United States breeding program would be bred and serve into the twentieth century up to World War II.
Many of the horses that served the US military came from the open ranges of NW Nevada, NE California and Southern Oregon.
During World War I, and into World War II, military cavalry contractor Harry Winton (sometimes referenced as ‘Wilson’) would roundup horses from the area now known as Sheldon National Wildlife Refuge. The horses would then be loaded onto railroad cars and shipped to the East Cost. From there the horses would make a trip across the Atlantic ocean by ship. Horses that survived the journey had a bit placed in their mouths and began to pull artillery or serve as a cavalry mount.
American Mustangs served as cavalry remounts for our allies as well as the supply of horses dwindled as the conflict raged in Europe. The cost in horses lives was great.
It is estimated that a shipment of 500 American horses left to supply American and allied troops during World War I every 1.5 days (archive stat). It is estimated that nearly eight million horses died in World War I alone.
Just a Note:
If you watch the film “War Horse” keep in mind that more Mustangs served in the war than domestic horses.