The postwar era was defined by the Cold War struggle between the United States and the Soviet Union. The 1947 Truman Doctrine pledged U.S. support for nations threatened by communist expansion, formalizing the policy of containment that would guide American foreign policy for decades. Anti-communist hysteria at home gave rise to McCarthyism in the early 1950s, as Senator Joseph McCarthy accused Americans of disloyalty without evidence, ruining careers through blacklists and creating a climate of fear. President Dwight D. Eisenhower, the former Supreme Allied Commander, oversaw the construction of the Interstate Highway System, enforced school desegregation at Little Rock in 1957, and famously warned of the growing "military-industrial complex."
The struggle for civil rights reached a moral crescendo in the mid-twentieth century. The Supreme Court's 1954 Brown v. Board of Education decision declared racial segregation in public schools unconstitutional, overturning Plessy v. Ferguson. The 1955 to 1956 Montgomery Bus Boycott, sparked by Rosa Parks's arrest and led by a young Martin Luther King Jr., demonstrated the power of nonviolent mass protest. The Civil Rights Act of 1964 outlawed discrimination based on race, color, religion, sex, or national origin, and the Voting Rights Act of 1965 dismantled barriers that had disenfranchised Black voters, dramatically expanding political participation. President Lyndon B. Johnson's Great Society programs added Medicare, Medicaid, the Elementary and Secondary Education Act, and the Immigration and Nationality Act of 1965, which transformed the nation's demographic future.
Abroad, the Cold War played out in Vietnam, where the 1964 Gulf of Tonkin Resolution authorized massive escalation of U.S. military involvement. The war killed over 58,000 Americans, divided society, sparked massive anti-war protests, and eroded trust in government, ending in failure and a reluctance to commit troops abroad known as the "Vietnam Syndrome." President John F. Kennedy, who had advanced the space program and the Peace Corps before his 1963 assassination, set the stage for NASA's Apollo program, which landed astronauts Neil Armstrong and Buzz Aldrin on the moon on July 20, 1969, a Cold War triumph for the United States. Domestic scandals also tested American institutions: the 1972 Watergate break-in and President Richard Nixon's subsequent cover-up led to his resignation in August 1974, the only presidential resignation in U.S. history, and the 1973 Roe v. Wade decision established a constitutional right to abortion until it was overturned in 2022.
President Ronald Reagan (1981 to 1989) pursued tax cuts, deregulation, military buildup, and a confrontational stance toward the Soviet Union, while his administration was tainted by the Iran-Contra Affair, in which officials secretly sold arms to Iran and diverted profits to Contra rebels in Nicaragua. The fall of the Berlin Wall in 1989 and the dissolution of the Soviet Union in 1991 left the United States as the world's sole superpower. The twenty-first century brought new challenges. On September 11, 2001, al-Qaeda terrorists killed nearly 3,000 Americans in attacks on the World Trade Center and Pentagon, prompting the wars in Afghanistan (2001 to 2021) and Iraq (2003 to 2011), the creation of the Department of Homeland Security, and the passage of the Patriot Act. The 2008 financial crisis, triggered by the collapse of a housing bubble and risky mortgage-backed securities, caused the worst recession since the Great Depression and led to massive bank bailouts. President Barack Obama, the first African American president, signed the Affordable Care Act in 2010 to expand health insurance coverage and oversaw the killing of Osama bin Laden, while the broader struggle for equality first kindled at Seneca Falls and pursued through Reconstruction, Jim Crow, and the Civil Rights Movement continues to shape the nation's identity and aspirations.