Unless you lived through the Eisenhower era, it may be hard to imagine the impact of the on-screen sight of sneering high-school students challenging adults with switch-blades. But in 1950s America, killing was still seen as something rare and horrible, something done by soldiers in battle, by lawmen, by gangsters, or by the occasional psychopath.
    Homicides in movies, even those considered violent, were infrequent. Those films presented juvenile delinquency more as the thread of rebellion and disobedience than of outright violence.
    The idea of American teenagers as killers was beyond compression. The change in 1957 when a wave of teen-street-gang killing in New York City (22 in the first six months of the year) spurred the emergency deployment of six hundred Police Academy cadets in a war on teen street crime. Though teen violence soon lost its place in news headlines to other crises, it did not go away.
    Thirty-five years later America is in the grip of a violence epidemic that has transformed the country into one of the most dangerous nations on earth. The national homicide rate, corrected for population growth, increased almost exactly 100 percent from 1950 to 1990. In major cities the increase has been much higher. In Los Angeles County the 1953 homicide total was 82. In 1992, with a population almost doubled, the total was 2,512—an increase of over 1,000 percent. These are staggering increase by any measure, with the one-year toll for L.A. County exceeding the deaths in over fifteen years of conflict in Northern Ireland.
    Youth crime accounts for a disproportionate number of these killings. That's more than twice the number recorded a decade earlier, reflecting the fact, according to FBI reports, that the number of youths who committed murder with guns was up 79 percent in one decade. Clearly something has gone horribly wrong. In looking for a root cause, one of the most obvious differences in the social and cultural fabric between post-World War Ⅱ and pre-World War Ⅱ America is the massive and pervasive exposure of American youth to television. Since the 1950s, behavioral scientists and medical researchers have been examining screen violence as a possible causative element in America's spiraling violent crime rate. There is compelling evidence of a direct, demonstrable link. Homicide has become the second leading cause among African-American youth. In 1992 the US surgeon general cited violence as the leading cause of injury to women aged 15 to 44, and the US Centers for Disease Control consider violence a public health issue, to be treated as an epidemic.  From the passage we can infer that ______.