April 25

Spartan forces under Lysander complete the blockade of Athens, bringing the Peloponnesian War to an end.

Spartan admiral Lysander, supported by King Pausanias, completed a naval and land blockade that starved Athens into submission, bringing the 27-year Peloponnesian War to an end with Sparta's decisive victory. The defeat stripped Athens of its empire and navy and marked the end of the city's golden age of democratic and cultural dominance in the ancient Greek world.

Nicolas J. Pelletier becomes the first person executed by guillotine in France.

Nicolas Jacques Pelletier, convicted of robbery and murder, became the first person executed by the newly adopted guillotine in France, a device intended by revolutionary reformers to provide a swifter, more humane, and more egalitarian method of execution than earlier practices. The guillotine subsequently became infamous as the primary instrument of execution during the Reign of Terror.

British and French engineers break ground on the Suez Canal, a project that would transform global maritime trade.

French and British engineers broke ground on construction of the Suez Canal in Egypt, a massive infrastructure project designed to connect the Mediterranean and Red Seas, eliminating the need for ships to sail around the entirety of Africa. Completed a decade later, the canal transformed global shipping routes and became a strategically vital, and frequently contested, waterway.

Allied forces land at Gallipoli, beginning a grueling and ultimately unsuccessful campaign against the Ottoman Empire during World War I.

Allied troops from Britain, France, Australia, New Zealand, and India landed at multiple beaches on Turkey's Gallipoli Peninsula, beginning a campaign intended to knock the Ottoman Empire out of World War I by seizing control of the strategically vital Dardanelles strait. The costly, ultimately unsuccessful eight-month campaign became a defining, formative national memory for Australia and New Zealand.

American and Soviet reconnaissance troops meet at the Elbe River in Germany, symbolically splitting Nazi forces in two.

American and Soviet reconnaissance patrols made contact near Torgau on the Elbe River in Germany, a symbolic meeting later commemorated as "Elbe Day" that visibly demonstrated the encirclement and impending collapse of Nazi Germany from both the east and west just days before Hitler's suicide and the war's end in Europe.

Delegates from 50 nations open the United Nations Conference on International Organization in San Francisco, drafting the UN Charter.

Delegates from 50 Allied nations convened in San Francisco for the United Nations Conference on International Organization, beginning weeks of negotiations that produced the United Nations Charter, establishing a new international body intended to prevent future global conflicts following the catastrophic failures that preceded both world wars.

James Watson and Francis Crick publish their landmark paper describing the double helix structure of DNA.

Molecular biologists James Watson and Francis Crick published a landmark paper in the journal Nature describing the double helix structure of DNA, building on crucial X-ray diffraction data produced by researcher Rosalind Franklin. The discovery revolutionized biology and medicine, laying the foundation for the fields of molecular genetics and modern biotechnology.

The Saint Lawrence Seaway officially opens, connecting the Great Lakes to the Atlantic Ocean for oceangoing vessels.

The Saint Lawrence Seaway, a system of canals, locks, and channels jointly developed by the United States and Canada, officially opened, allowing oceangoing vessels to travel from the Atlantic Ocean deep into North America's Great Lakes for the first time. The massive engineering project transformed industrial and agricultural shipping across the region.

A leftist military coup in Portugal, the Carnation Revolution, overthrows the authoritarian Estado Novo regime.

A group of left-leaning Portuguese military officers staged a largely bloodless coup that overthrew the decades-old authoritarian Estado Novo regime, an uprising that became known as the Carnation Revolution after citizens placed flowers in soldiers' rifle barrels. The revolution restored democracy to Portugal and precipitated the rapid decolonization of its African territories.

A magnitude 7.8 earthquake strikes Nepal, killing nearly 9,000 people and devastating the Kathmandu Valley.

A massive magnitude 7.8 earthquake struck near Kathmandu, Nepal, triggering deadly avalanches on Mount Everest and collapsing thousands of buildings across the densely populated region, ultimately killing nearly 9,000 people and displacing hundreds of thousands more. The disaster prompted a large international humanitarian response and years of rebuilding efforts.