Following the 1830 Belgian Revolution that split the country from the Kingdom of the Netherlands, the National Congress offered the crown to Leopold of Saxe-Coburg, a widower of Britain's Princess Charlotte. He accepted a constitutional monarchy with limited powers, and July 21 became Belgium's National Day, still celebrated with a military parade in Brussels.

At just 21 years old, Colt patented a pistol with a rotating cylinder holding multiple chambers, allowing several shots without reloading. The mechanism, reportedly inspired by watching a ship's wheel lock into place, became the basis for Colt's Patent Arms Manufacturing Company and made 'Colt' a household name synonymous with the American frontier.

Union troops under General Irvin McDowell advanced confidently, watched by curious civilian spectators who'd ridden out from Washington expecting a quick victory. Confederate reinforcements arriving by rail helped turn the tide, and the Union retreat collapsed into a chaotic rout back toward the capital, revealing that both untrained armies, and the public, had badly underestimated the war ahead.

Bingham, a Yale lecturer searching for the lost city of Vilcabamba, was led up a steep Peruvian ridge by an 11-year-old boy and his father, farmers who already knew the site. He found stone terraces and temples swallowed by jungle vines, later publishing photographs that made Machu Picchu one of the most famous archaeological sites on Earth.

Commissioned by the Spanish Republican government for the Spanish Pavilion, Picasso's enormous canvas depicted the suffering caused by the German and Italian bombing of Guernica during the Spanish Civil War. Initially met with mixed reviews, the painting later became one of the twentieth century's most powerful anti-war symbols, touring the world for decades before settling in Madrid.

Negotiated after France's defeat at Dien Bien Phu, the accords split Vietnam into a communist north under Ho Chi Minh and a nominally independent south, with reunification elections promised within two years that never took place. The United States, wary of communist expansion, declined to sign, deepening its own commitment to prevent Southern collapse in the years that followed.

At 2:56 UTC, Neil Armstrong descended the Eagle's ladder and became the first human to touch another world. Buzz Aldrin followed twenty minutes later, and the two spent nearly two and a half hours collecting samples, planting a flag, and testing how the body moved under one-sixth gravity, while Michael Collins orbited alone above in the command module Columbia.