Early in 1939, the world's scientific community discovered that German physicists had learned the secrets of splitting a uranium atom. Fears soon spread over the possibility of Nazi scientists utilizing that energy to produce a bomb capable of unspeakable destruction. The Allies had to beat the Nazis to the punch.

When Harry Truman learned of the success of the Manhattan Project, he knew he was faced with a decision of unprecedented gravity. The capacity to end the war with Japan was in his hands, but it would involve unleashing the most terrible weapon ever known.

After the end of World War II, no single foreign policy issue mattered more to the United States for the next 50 years as much as the Cold War. President Truman set the direction for the next eight presidents with the announcement of the containment policy. Crises in Berlin, China, and Korea forced Truman to back his words with actions. The Cold War kept defense industries humming and ultimately proved the limits of American power in Vietnam. Democracy was tested with outbreaks of Communist witch hunts.

In 1945, one major war ended and another began. The Cold War lasted about 45 years. There were no direct military campaigns between the two main antagonists, the United States and the Soviet Union. Yet billions of dollars and millions of lives were lost in the fight.

Despite the ideological animosity spawned by the Cold War, a new spirit of globalism was born after WWII. It was based, in part, on the widespread recognition of the failures of isolationism. The incarnation of this global sprit came to life with the establishment of the United Nations in 1945 with its headquarters in New York City.

Communism was on the march. A mid-level diplomat in the State Department named George Kennan proposed the policy of containment. Since the American people were weary from war and had no desire to send United States troops into Eastern Europe, rolling back the gains of the Red Army would have been impossible. But in places where communism threatened to expand, American aid might prevent a takeover. By vigorously pursuing this policy, the United States might be able to contain communism within its current borders.

Berlin, Germany's wartime capital was the prickliest of all issues that separated the United States and Soviet Union during the late 1940s. The city was divided into four zones of occupation like the rest of Germany. However, the entire city lay within the Soviet zone of occupation. Once the nation of East Germany was established, the Allied sections of the capital known as West Berlin became an island of democracy and capitalism behind the Iron Curtain.

Containment had not gone so well in Asia. When the Soviet Union entered the war against Japan, they sent troops into Japanese-occupied Korea. As American troops established a presence in the southern part of the Korean peninsula, the Soviets began cutting roads and communications at the 38th parallel. Two separate governments were emerging, as Korea began to resemble the divided Germany.

The end of World War II brought a series of challenges to Harry Truman. The entire economy had to be converted from a wartime economy to a consumer economy. Strikes that had been delayed during the war erupted with a frenzy across America. Inflation threatened as millions of Americans planned to spend wealth they had not enjoyed since 1929. As the soldiers returned home, they wanted their old jobs back, creating a huge labor surplus. Truman, distracted by new threats overseas, was faced with additional crises at home.

A booming economy helped shape the blissful retrospective view of the 1950s. A rebuilding Europe was hungry for American goods, fueling the consumer-oriented sector of the American economy. Conveniences that had been toys for the upper classes such as fancy refrigerators, range-top ovens, convertible automobiles, and televisions became middle-class staples.

Senator Joseph McCarthy rose to national prominence by initiating a probe to ferret out communists holding prominent positions. During his investigations, safeguards promised by the Constitution were trampled.

Racial fears, affordable housing, and the desire to leave decaying cities were all factors that prompted many white Americans to flee to suburbia. And no individual promoted suburban growth more than William Levitt.

Perhaps no phenomenon shaped American life in the 1950s more than television. At the end of World War II, the television was a toy for only a few thousand wealthy Americans. Just 10 years later, nearly two-thirds of American households had a television.

This generation of youth was much larger than any in recent memory, and the prosperity of the era gave them money to spend on records and phonographs. By the end of the decade, the phenomenon of rock and roll helped define the difference between youth and adulthood. Rock and roll sent shockwaves across America. A generation of young teenagers collectively rebelled against the music their parents loved. In general, the older generation loathed rock and roll. Appalled by the new styles of dance the movement evoked, churches proclaimed it Satan's music.

As the British and French Empires slowly yielded to independence movements, a new Third World emerged. This became the major battleground of the Cold War as the United States and the Soviet Union struggled to bring new nations into their respective orbits. Across the Third World, the two superpowers squared off through proxy armies.

Many in the 1950s strove for the comfort and conformity depicted on such TV shows as Father Knows Best and Leave It to Beaver. But despite the emerging affluence of the new American middle class, there was a poverty, racism, and alienation in America that was rarely depicted on TV.

Despite the efforts of Radical Reconstructionists, the American South emerged from the Civil War with a system of laws that undermined the freedom of African Americans and preserved many elements of white privilege. No major successful attack was launched on the segregation system until the 1950s.

In the aftermath of World War II, America sought to demonstrate to the world the merit of free democracies over communist dictatorships. But its segregation system exposed fundamental hypocrisy. Change began brewing in the late 1940s. President Harry Truman ordered the end of segregation in the armed services, and Jackie Robinson became the first African American to play Major League Baseball. But the wall built by Jim Crow legislation seemed insurmountable.

On a cold December evening in 1955, Rosa Parks quietly incited a revolution — by just sitting down on the bus.

Three years after the Supreme Court declared race-based segregation illegal, a military showdown took place in Little Rock, Arkansas, when nine black students attempted to attend the all-white Central High School on September 3, 1957.