1941 - On 7 December , Japanese warplanes attack the US fleet at Pearl Harbour in Hawaii. The US declares war on Japan the following day and enters World War Two.

1945 - The US drops an atomic bomb on Hiroshima on August 6 and another on Nagasaki three days later. Japan surrenders on 2 September.

The United Nations, comprising 51 original members but expanding to 188 by 2000, replaces the failed League of Nations. The US plays a leading role in its formation.

1948 - The US launches the Marshall Plan, a programme of economic aid to revive the ailing post-war European economies. President Harry Truman ends racial segregation in the US military.

1949 The North Atlantic Treaty Organisation (Nato), an alliance of 12 original members, is established in response to the threat posed by the Soviet Union. Each member promises to treat an attack on a fellow member as an attack on themselves. Nato is expanded to include other countries at later dates.

1950-54 - Senator Joseph McCarthy carries out a crusade against alleged communists in government and public life. The campaign and its methods become known as "McCarthyism". In 1954 McCarthy is formally censured by the Senate.

1950-53 - The United Nations declares war on North Korea and US forces play a leading role against North Korean and Chinese troops.

1951 The US maximum presidency term is restricted to eight years.

1955 - The first McDonalds restaurant is opened.

1957 - President Dwight Eisenhower sends troops to Little Rock, Arkansas, to enforce the desegregation of schools.

1957-69 - The Sputnik is launched by the Soviets and is the first artificial satellite to orbit the earth. This marks the beginning of the great space race between the Soviet Union and the US. Soviet astronaut Yuri Gagarin becomes the first man in space in 1961, but America wins the race to the Moon in 1969.

1959 - The US severs its diplomatic links with Cuba after Fidel Castro rises to power and Cuba becomes a communist state.

1960 - Democratic Party candidate John F Kennedy is elected as president, narrowly defeating his rival Richard Nixon.

Four African American students stage a sit-in at the FW Woolworth store in Greensboro, North Carolina, to protest at segregation at its lunch counter.

1961 - Washington organises and finances an unsuccessful attempt to invade Cuba by Cuban exiles in the Bay of Pigs.

1962 - The US compels the Soviet Union to withdraw nuclear weapons from Cuba in what has become known as the "Cuban missile crisis".

1963 - President John F Kennedy is assassinated and Lyndon Johnson becomes president.

Hundreds of thousands of people take part in the March on Washington to call for racial equality.

1964 - After the attacks on US destroyers in the Tonkin Gulf, Vietnam, Congress responded with the Tonkin Gulf Resolution, expressing support for "all necessary measures" to repel armed attacks against US forces and prevent further aggression. The US steps up its military intervention in Vietnam war.

The Civil Rights Act gives African-Americans constitutional equality and outlaws discrimination in public accommodations and by employers.

1965 - Black leader Malcom X is assassinated in New York. The Voting Rights Act nullifies local laws and practices that prevent minorities from voting.

1966 - The Black Panther party, a black rights group, is founded.

1968 - Black civil rights leader Martin Luther King assassinated. Robert Kennedy, brother of JFK, is also assassinated.

1969 - Republican Party candidate Richard Nixon is elected as president amid growing public opposition to Vietnam war.

US astronaut Neil Armstrong becomes the first person to walk on the Moon, with the line: "One small step for man; one giant leap for mankind."

1972 - Nixon is re-elected and makes an historic visit to China.

1973 - A Vietnam ceasefire agreement is signed and US forces pull out of Vietnam to end a campaign that has cost 58,000 American lives.

1974 - In a TV address, President Nixon announces his resignation in the wake of the Watergate scandal, over a 1972 break-in at the Democratic Party headquarters. Gerald Ford is sworn-in as his successor.

1976 - Democratic Party candidate Jimmy Carter is elected as President.

1979 - The US embassy in Tehran, Iran, is seized by radical students. The hostage crisis - including a failed rescue attempt in 1980 - impacts on Carter's popularity and dominates the 1980 presidential election campaign.

1980 Republican Ronald Reagan is elected as president. Reagan goes on to adopt a tough anti-communist foreign policy and tax-cutting policies.

1981 Iran frees the US embassy hostages. Reagan is shot in the chest but survives the assassination attempt.

1982 - Reagan deploys marines to serve in a temporary multinational force in Lebanon.

1983 - The US invades Caribbean the nation of Grenada, partly prompted by its concerns over the island's ties with Cuba.

1984 - Reagan is re-elected as president, beating Democratic Party candidate Walter Mondale. The Macintosh computer with a mouse is launched.

1986 The Space shuttle Challenger explodes shortly after take off from Cape Canaveral. All seven crew members are killed and manned space flights are suspended.

US warplanes bomb Libyan cities. The "Irangate" scandal is uncovered, revealing that proceeds from secret US arms sales to Iran were used illegally to fund Contra rebels in Nicaragua.

1988 - Reagan's vice-president, George Bush, is elected as president.

1989 - US troops invade Panama, oust its government and arrest its leader, one-time Central Intelligence Agency informant General Manuel Noriega, on drug-trafficking charges.

The Berlin Wall comes down, ending an era of Communist rule in eastern Europe and leading to the collapse of the Soviet Union.

1991 - US forces play a dominant role in war against Iraq, which was triggered by Iraq's invasion of Kuwait and ended with the expulsion of Iraqi troops from that country.