1969: Urban America is still recovering from the race riots that devastated Baltimore, Boston, Kansas City, Newark, Chicago, Washington D.C., Detroit, and other cities the previous summer, following the assassination of civil rights leader Martin Luther King Jr.

Today: Many civil rights organizations continue to try to combat racial inequities in America.

1969: Many American youths of all social classes are united in their opposition to the war in Vietnam, creating a "youth culture" that spreads hippie styles, music, and slogans.

Today: Many American youths identify with styles, music, and slogans that they receive from the media, such as movies, television shows, music videos, and commercials.

1969: The country becomes aware of heroin, as sales of the drug skyrocket among schoolchildren. The government's new Operation Intercept program is so successful that heroin suddenly becomes competitively priced.

Today: After dropping by more than half between 1975 and 1990, heroin...