1940s: The beginnings of the Cold War between the United States and the Soviet Union create an uneasy current of fear and doubt in an otherwise hopeful and complacent post-World War II United States. The conflict involves massive arms buildup by both nations, including nuclear warheads—the most worrisome aspect of the Cold War. Today: The United States and Russia are allies in the war on terrorism, although President George W. Bush's decision to withdraw from the 1972 Anti-Ballistic Missile Treaty, which forbids testing and deployment of a ballistic missile defense system, greatly concerns Russian officials.

1940s: In an effort to flee the crime and "unsavory" elements of the big city, many Americans head to the suburbs. In Long Island, New York, builders erect Levittown, a middle-class suburb with prefabricated housing materials, the first of its kind. Over the next decade, land values increase, sometimes...