Why did cowtowns find it necessary to "keep the peace"? how did they go about doing this?

By the end of Civil War, as many as five million longhorn cattle, descendants of old Spanish stock, roamed wild in Texas. These tough, rangy animals sported horns with a spread of as much as eight feet. At first they were hunted only for their hides since there was no way to get them to markets in the East. With the building of the Transcontinental Railroads, it became possible to transport these cattle to the eastern market that had developed a taste for beef at a time when the effects of war had depleted eastern herds. Beef, even tough wild beef, was in great demand. 

- Radical Dead