On or about August 20, 1619, “20 and odd” Angolans, kidnapped by the Portuguese, arrive in the British colony of Virginia and are then bought by English colonists. The exact date is not definitively known (a letter from the time identified the ship's arrival coming in "the latter part of August"), but this date has been chosen by many to mark the arrival of the enslaved Africans in the New World—beginning two and a half centuries of slavery in North America.

Sergeant Charles Floyd dies three months into the voyage of Meriwether Lewis and William Clark, becoming the only member of the Corps of Discovery to die during the journey.

New York Tribune editor Horace Greeley publishes a passionate editorial calling on President Abraham Lincoln to declare emancipation for all enslaved people in Union-held territory. Greeley’s blistering words voiced the impatience of many Northern abolitionists; but unbeknownst to Greeley and the public, Lincoln was already moving in the direction of emancipation.

On August 20, 1911, a dispatcher in the New York Times office sends a blazingly fast telegram around the world via commercial service. Exactly 66 years later, the National Aeronautics and Space Administration (NASA) sends a different kind of message—a phonograph record containing information about Earth for extraterrestrial beings—shooting into space aboard the unmanned spacecraft Voyager II.

Exiled Russian revolutionary Leon Trotsky is fatally wounded by an ice-ax-wielding assassin at his compound outside Mexico City. The killer—Ramón Mercader—was a Spanish communist and probable agent of Soviet leader Joseph Stalin. Trotsky died from his wounds the next day.

On August 20, 1945, 11 days after the atomic bombing of Nagasaki, Japan, Brooklyn Dodgers utility player Tommy Brown homers to drive in his team's only run in an 11-1 loss to the Pittsburgh Pirates. It seems insignificant, aside from the fact that, at 17 years old, Brown remains the youngest player to homer in a Major League Baseball game, a feat unlikely to be duplicated.

President Eisenhower approves a National Security Council paper titled “Review of U.S. Policy in the Far East.” This paper supported Secretary of State Dulles’ view that, in light of U.S. fears of a regional attack by communist China, the United States should support Vietnamese prime minister Ngo Dinh Diem, while encouraging him to broaden his government and establish more democratic institutions. Ultimately, however, Diem would refuse to make any meaningful concessions or institute any significant new reforms and U.S. support was withdrawn. Diem was subsequently assassinated during a coup by opposition generals on November 2, 1963.

Viking 1, an unmanned U.S. planetary probe, is launched from Cape Canaveral, Florida, on a mission to Mars.