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.

On August 20, 1920, seven men, including legendary all-around athlete and football star Jim Thorpe, meet to organize a professional football league at the Jordan and Hupmobile Auto Showroom in Canton, Ohio. The meeting led to the creation of the American Professional Football Conference (APFC), the forerunner to the hugely successful National Football League.

On August 20, 1944, Soviet forces launch Second Jassy-Kishinev Offensive, an offensive in northeastern Romania in which they ultimately surround the invading German Sixth Army. One of the most successful, and little-remembered, joint operations between Soviet and American forces (who provided air support), the operation succeeded ultimately in convincing Romania’s king to sign an armistice with the Allies and concede control of his country to the USSR.

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.

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