...the book "Slavery: The African American Psychic Trauma," (Authors: Sultan Latif & Naimah Latif) explains why. An excerpt from the book states:
"America's police patrol actually grew out of the south. Up until that time, justice was administered by local sheriffs and deputies. After the Revolutionary War, most states developed some type of militia, in case armed soldiers were needed for national defense. But the institution of slavery required that some type of organized law enforcement would have to be instituted on a regular basis, to protect white slave owners against massive uprisings and escapes. In "From Slavery To Freedom," Franklin describes how the slave patrols worked: 'One of the devices set up to enforce the slave codes and thereby maintain the institution of slavery was the patrol, which has been aptly described as an adaptation of the militia. counties were usually divided into "beats" or areas of patrol, and free White men were called upon to serve for a stated period of time, 1, 3, or 6 months. These patrols were to apprehend slaves out of place and return them to their masters or commit them to jail; to visit slave quarters and search for various kinds of weapons that might be used in an uprising; and to visit assemblies of slaves where disorder might develop or where conspiracy might be planned.'"