1945: The United States has an arsenal of two bombs.

1961: Life Magazine offers tips on building bomb shelters, which has been urged by President Kennedy.

1962: Rachel Carson's Silent Spring, a book about how the use of DDT poisons the earth, is published. The resulting public outcry about pesticide use leads to changes in the laws affecting the air, land, and water, and launches the environmental movement as we know it today.

1963: Preaching nonviolence, Dr. Martin Luther King delivers his "I Have a Dream" speech in Washington, D.C.

1986: The Soviet nuclear reactor at Chernobyl melts down, releasing 10 times the radiation of the Hiroshima bombing. The Soviet Union's arsenal reaches 45,000.

1995: A Gallup poll shows that 60 percent of Americans surveyed cannot name the president who ordered the 1945 bombing of Japan. 22 percent don't know that bombs were dropped at all.

1997: A United Nations-sponsored conference on global warming is...