During the second half of the 19th century, the railroad tied the country together in fundamentally new ways. New cities, such as Atlanta and Chicago, grew rapidly as they became central to the evolving transportation system. Railroads connected previously isolated regions, increasing the importance of cities as centers of manufacturing and marketplaces for the goods of the hinterlands.

The lithograph "Twentieth Century Transportation" (circa 1910) was created when cities were still increasing in power and influence in the United States. It pictures most of the modes of transportation of that time: the railroad, streetcar, and ship and, in their infancy, the truck, automobile, blimp, and airplane. The automobile was the plaything of the rich in 1910, but a decade later it would begin its rise to transportation domination, transforming the city and leading to its decentralization. Unlike the subway, streetcar, and railroad, which brought people downtown, the car seemed destined for the open road leading out of town. The automobile created the modern suburb, with its easy-to-reach office parks and shopping centers set alongside the modern highway. One may question the long-term economic and environmental viability of the automobile in an era of global warming and high gasoline prices, but the car continues to draw people away from the city's center.