Communications media networks were born with the 1926 radio sign-on of the National Broadcasting Company (NBC), signaling the dawn of a new era of both communications and culture in America. The network concept is purely abstract—even in its practical form nothing but a series of wires or satellite connections. Yet the history and influence of the broadcast networks is one of the great stories of the twentieth century, for though they did not create it, the networks did cement the process of homogenizing American culture. By 1930, for the first time America was whistling to the same tunes, laughing at the same comedians, hearing the same politicians' speeches—instantaneously. The taste and judgement of a relative few urban, Northeastern network executives set national standards of everything from dialect and language to fashion and behavior. Only when the influence of the old-line networks had faded, by the end of the...