The 40's

World War II ended the Great Depression of the 1930's. During the 1930's three totalitarian, militaristic powers had arisen in the world--Germany, Italy, and Japan. Germany, under Adolph Hitler and the National Socialist (Nazi) Party, invaded Poland on September 1, 1939, and Britain and France declared war upon Germany and its allies two days later. By the summer of 1940, the Nazi Blitzkrieg , or lightening war, had rolled over Denmark, Norway, the Netherlands, Belgium, and France, giving Germany control of most of western Europe. Italy declared war in June 1940, and invaded British and French Somaliland, Egypt, and Greece later that summer. Germany, Italy, and Japan signed the Tripartite Pact, making them allies, in September 1940. In the Far East, Japan had marched through China, reaching French Indochina (now Vietnam) by July 1941.

The United States, however, remained neutral until December 1941. Since the close of World War I, the United States had striven to isolate itself politically from what it saw as internal European problems. President Roosevelt announced, "This nation will remain a neutral nation, but I cannot ask that every American remain neutral in thought as well." The United States remained neutral in neither thought nor action. It sold surplus weapons and traded aging destroyers to the British in exchange for military bases.

• December 1941

  Japan bombs Pearl Harbor. The United States enters World War II.

• September 1942

  The Manhattan Project is formed to secretly build the atomic bomb before the Germans.

• November 1942

  Los Alamos is selected as the site for an atomic bomb laboratory. Robert Oppenheimer is named the director.

• December 1942

  Fermi demonstrates the first self-sustaining nuclear chain reaction in a lab under the squash court at the University of Chicago. Soon after, a complex of top-secret nuclear production and research facilites are built by the Manhattan Project across the country.

• 1942-45

  The Clinton Engineer Works is built in Oak Ridge, Tennessee. It is renamed the Oak Ridge National Laboratory after World War II. The Clinton Pile, the first true plutonium production reactor, begins operation in November 1943. By March 1945, K-25 and other gaseous diffusion plants are in operation.

• 1943-45

  The Hanford Site is built in Richland, Washington by the Manhattan Project to produce plutonium. The first reactor begins operation in September 1944.

• February 1945

  Yalta Summit ratifies a divided postwar Europe.

• April 1945

  U.S. troops liberate Nazi concentration camp at Buchenwald.

• May 1945

  Germany surrenders.

• July 1945

  The United States explodes the first atomic device at a site near Alamagordo, New Mexico.

• August 1945

  The United States drops atomic bombs on Hiroshima and Nagasaki. Japan surrenders.

• March 1946

  Winston Churchill proclaims an "iron curtain" has come down across Europe.

• July 1946

  Atomic Energy Act (AEA) is passed, establishing the Atomic Energy Commission (AEC). The AEC replaces the Manhattan Project on December 31, 1946. The AEA places further development of nuclear technology under civilian (not military) control.

• July 1946

  The United States tests a nuclear bomb on Bikini Atoll, an island in the Pacific. Four days later bikini swimsuit debuts at a French fashion show.

• August 1946

  The Oak Ridge facility ships the first nuclear reactor-produced radioisotopes for civilian use to the Barnard Cancer Hospital in St. Louis. After World War II, Oak Ridge turns out numerous inexpensive radioactive compounds for medical diagnosis and treatment, and for research and industrial applications.

• April-May 1948

  Nuclear tests in the South Pacific (Operation Sandstone) pave the way for mass production of weapons that previously had to be assembled by hand. By late 1948, the United States has 50 nuclear bombs.

• June 1948

  The Soviet Union begins the Berlin Blockade, cutting West Berlin off from the West. The United States begins vast airlift to keep Berlin supplied with food and fuel.

• May 1949

  National Chinese forces led by Chiang Kai-shek retreat from mainland China to Formosa.

• August 1949

  The Soviet Union detonates its first atomic device.