1930s: Many street gangs that arose during the 1920s in order to take advantage of Prohibition move on to other illegal ventures. The romanticized "Dead End Kids" (also known as the East Side Kids and the Bowery Boys) star in a number of movies during this time.

1990s: Gang members range from grade-school children to adults. Drug dealing and related crimes are a major activity and means of profit for gangs In Los Angeles alone, there are an estimated 70,000 gang members. In 1997, a new California program attempts to curtail gang violence by bringing criminal charges against parents of gang members. The program makes use of a 90-year-old law requiring the reasonable care and supervision of children.

1930s: During the Great Depression, murder rates are considered high. They peak in 1933 at 9.7 murders per 100,000 people annually.

1990s: Murder rates begin to fall in urban areas after...