1950s: In the midst of the Cold War, Americans are fearful of a nuclear attack by the Soviet Union. Fallout shelters are designed and built, and school children regularly practice "duck and cover" procedures in the event of an air raid.

Today: After the September 11, 2001, terrorist attacks on New York City and Washington, D.C., many Americans live in fear that terrorists may strike again at any time, anywhere in the country. Security firms offer classes for civilians in how to disarm a potential terrorist on an airplane.

1950s: The Soviet Union and the United States engage in a Cold War as two enemies with nuclear capability, each stockpiling weapons in an attempt to achieve nuclear superiority.

Today: The Soviet Union has separated into individual countries; the largest of these, Russia, is now an ally of the United States in the space program and...