By serving travelers and commerce, roads and streets unite people and foster economic growth. But as they develop, roads and streets also disrupt old patterns, upset balances of power, and isolate some as they serve others. The consequent disagreements leave historical records documenting social struggles that might otherwise be overlooked. For long-distance travel in America before the middle of the 20th century, roads were generally poor alternatives, resorted to when superior means of travel, such as river and coastal vessels, canal boats, or railroads were unavailable. Most roads were unpaved, unmarked, and vulnerable to the effects of weather. Before the railroads, for travelers willing to pay the toll, rare turnpikes and plank roads could be much better. Even in towns, unpaved streets were common until the late 19th century, and persisted into the 20th. In the late 19th century, rapid urban growth, rural free delivery of the mails, and finally the proliferation of electric railways and bicycling contributed to growing pressure for better roads and streets. After 1910, the spread of the automobile accelerated the trend, but only with great controversy, especially in cities. Partly in response to the controversy, advocates of the automobile organized to promote state and county motor highways funded substantially by gasoline taxes; such roads were intended primarily for motor vehicles. In the 1950s, massive federal funds accelerated the trend; by then, motor vehicles were the primary transportation mode for both long and short distances. The consequences have been controversial, and alternatives have been attracting growing interest.
Rioting in the United States since 1800 has adhered to three basic traditions: regulating communal morality, defending community from outside threats, and protesting government abuse of power. Typically, crowds have had the shared interests of class, group affiliation, geography, or a common enemy. Since American popular disorder has frequently served as communal policing, the state—especially municipal police—has had an important role in facilitating, constraining, or motivating unrest.
Rioting in the United States retained strong legitimacy and popular resonance from 1800 to the 1960s. In the decades after the founding, Americans adapted English traditions of restrained mobbing to more diverse, urban conditions. During the 19th century, however, rioting became more violent and ambitious as Americans—especially white men—asserted their right to use violence to police heterogeneous public space. In the 1840s and 1850s, whites combined the lynch mob with the disorderly crowd to create a lethal and effective instrument of white settler sovereignty both in the western territories and in the states. From the 1860s to the 1930s, white communities across the country, particularly in the South, used racial killings and pogroms to seize political power and establish and enforce Jim Crow segregation. Between the 1910s and the 1970s, African Americans and Latinos, increasingly living in cities, rioted to defend their communities against civilian and police violence. The frequency of rioting declined after the urban rebellions of the 1960s, partly due to the militarization of local police. Yet the continued use of aggressive police tactics against racial minorities has contributed to a surge in rioting in US cities in the early 21st century.