Only in the mid-nineteenth century, after the growth of industrial cities and a rash of urban riots—after dread of the so-called dangerous classes surpassed dread of the state—did police departments emerge in the United States. By the time of Anna’s death, the informal system of citizen policing had been displaced, but vestiges of it remained, especially in places that still seemed to exist on the periphery of geography and history.
-- David Grann (chapter 2 paragraph 2)

Importance: This explains the limited role the professional police forces played in American history, particularly in remote areas like Osage County.

The U.S. government, contending that many Osage were unable to handle their money, had required the Office of Indian Affairs to determine which members of the tribe it considered capable of managing their trust funds. Over the tribe’s vehement objections, many Osage, including Lizzie and Anna, were deemed 'incompetent,' and were forced to have...
-- David Grann, quoting a member of the Osage tribe (chapter 5 paragraph 1)