April 13

Constantinople falls to the Fourth Crusade after the sack of the city, temporarily ending the Byzantine Empire and installing a Latin emperor.

After breaching the city's walls the previous day, soldiers of the Fourth Crusade completed their conquest of Constantinople, subjecting the Byzantine capital to a brutal sack that included widespread looting, destruction, and violence against its Christian residents. The crusaders installed a Latin emperor over the fractured remains of the Byzantine Empire, a division that persisted for decades and permanently weakened Byzantine power.

Guru Gobind Singh formally establishes the Khalsa, a defining institution of the Sikh faith, in northern India.

Guru Gobind Singh, the tenth Sikh guru, formally established the Khalsa, a collective religious community bound by a distinct code of conduct and identity, during a gathering at Anandpur Sahib in Punjab. The founding of the Khalsa remains one of the most significant events in Sikh history, and its anniversary is celebrated annually as the festival of Vaisakhi.

George Frideric Handel's oratorio "Messiah" receives its world premiere in Dublin, Ireland.

George Frideric Handel's oratorio "Messiah," now among the most frequently performed choral works in the Western musical canon, received its world premiere at a charity concert in Dublin, Ireland, to great acclaim. The piece, including its famous "Hallelujah" chorus, was composed in an astonishingly short period of about three weeks and has become a staple of Christmas and Easter concert programs worldwide.

Union forces surrender Fort Sumter to Confederate troops after a 34-hour bombardment.

After a sustained 34-hour bombardment by Confederate artillery, the Union garrison at Fort Sumter, commanded by Major Robert Anderson, surrendered the fort without any fatalities from the shelling itself, though the formal surrender ceremony the next day claimed the war's first casualties in an accidental explosion. The fort's fall marked the opening chapter of the American Civil War.

The Metropolitan Museum of Art is founded in New York City.

A group of prominent American civic leaders and philanthropists founded the Metropolitan Museum of Art in New York City, intending to bring great works of art to American audiences and foster art education. Since opening its doors a few years later, the museum has grown into one of the largest and most visited art museums in the world.

British troops kill hundreds of unarmed demonstrators at the Jallianwala Bagh massacre in Amritsar, India, galvanizing the Indian independence movement.

British Indian Army troops under General Reginald Dyer opened fire without warning on a large, peaceful crowd of unarmed demonstrators gathered in an enclosed public garden in Amritsar, India, killing hundreds and wounding many more. The Jallianwala Bagh massacre became a pivotal moment that galvanized widespread Indian outrage and significantly strengthened the movement for independence from British colonial rule.

Nazi Germany announces the discovery of mass graves of Polish officers killed by Soviet forces in the Katyn Forest.

Nazi German authorities publicly announced the discovery of mass graves in the Katyn Forest near Smolensk containing the remains of thousands of Polish military officers, using the finding for propaganda purposes to drive a wedge between the Soviet Union and its Western Allies. The Soviet Union, in fact responsible for the massacre, denied involvement for decades until finally admitting responsibility in 1990.

An oxygen tank explodes aboard Apollo 13, forcing NASA to abort the Moon landing and focus on returning the crew safely to Earth.

An oxygen tank aboard the Apollo 13 spacecraft exploded roughly 200,000 miles from Earth, crippling the vessel's power and life support systems and forcing NASA to abandon the planned Moon landing in favor of an urgent effort to bring the three astronauts home alive. The subsequent rescue, achieved through resourceful improvisation, became one of the most celebrated episodes in spaceflight history.

A deadly attack on a bus in Beirut marks the start of Lebanon's 15-year civil war.

A bus carrying Palestinian passengers was ambushed and attacked by Christian Phalangist militiamen in a Beirut suburb, killing around two dozen people in an incident widely regarded as the spark that ignited Lebanon's devastating 15-year civil war. The conflict that followed drew in numerous regional and international powers and left the country deeply fractured along sectarian lines for decades.

Tiger Woods wins the Masters Tournament by a record 12 strokes, becoming the youngest champion in the event's history.

A 21-year-old Tiger Woods won the Masters Tournament by a record-setting 12 strokes, becoming both the youngest golfer ever to win the event and the first player of Black or Asian heritage to claim a major championship. His dominant, record-breaking performance signaled the arrival of a talent that would go on to reshape the sport of golf over the following two decades.