April 22

Pope Gregory VII is elected, later becoming a central figure in the Investiture Controversy with the Holy Roman Empire.

German-born cardinal Gregory VII was elected pope by popular acclamation following the death of his predecessor, going on to become a central figure in the Investiture Controversy, a decades-long power struggle with Holy Roman Emperor Henry IV over whether secular rulers or the papacy held authority to appoint bishops.

Portuguese navigator Pedro Álvares Cabral becomes the first European to reach Brazil.

Portuguese navigator Pedro Álvares Cabral, commanding a fleet bound for India, made landfall on the coast of present-day Brazil, becoming the first European to document the territory, which Portugal subsequently claimed and colonized. Some historians debate whether the landing was accidental, caused by ocean currents, or a deliberate exploratory detour.

Hernán Cortés establishes the settlement of Veracruz on the Mexican coast, his base for the conquest of the Aztec Empire.

Spanish conquistador Hernán Cortés established the settlement of Veracruz on the Gulf coast of Mexico, using it as a strategic base of operations for his subsequent inland campaign against the Aztec Empire. The founding of Veracruz also symbolically allowed Cortés to declare independence from the authority of the Cuban governor who had commissioned his expedition.

Napoleon's forces defeat Austria at the Battle of Eckmühl during the War of the Fifth Coalition.

Napoleon's forces decisively defeated the Austrian army at the Battle of Eckmühl in Bavaria during the War of the Fifth Coalition, splitting Austrian forces and forcing a retreat that allowed Napoleon to advance toward Vienna. The victory reinforced Napoleon's reputation as Europe's preeminent military commander at the height of his power.

The first National League baseball game is played in Philadelphia, marking the start of the oldest surviving major professional sports league in the U.S.

The Boston Red Stockings and Philadelphia Athletics played the first official game of baseball's newly formed National League in Philadelphia, establishing what remains the oldest continuously operating professional sports league in the United States and a foundational institution in the development of American baseball.

Tens of thousands of settlers rush to claim land in the Land Run of 1889, instantly creating cities like Oklahoma City and Guthrie.

Tens of thousands of settlers lined up at the border of unassigned lands in Indian Territory and rushed in at the sound of a signal to stake claims, instantly transforming stretches of open prairie into settlements including what became Oklahoma City and Guthrie in what became known as the Land Run of 1889.

German forces release chlorine gas at the Second Battle of Ypres, the first large-scale use of chemical weapons in warfare.

German forces released chlorine gas against French and colonial troops at the Second Battle of Ypres, the first large-scale use of chemical weapons in modern warfare, creating panic and mass casualties among unprotected soldiers. The attack marked a grim escalation in the brutality of World War I and prompted the rapid development of gas masks and countermeasures.

The first Earth Day is celebrated across the United States, mobilizing millions and helping launch the modern environmental movement.

An estimated 20 million Americans participated in the first Earth Day, organized by Senator Gaylord Nelson and activist Denis Hayes through rallies, teach-ins, and cleanups across the country, mobilizing public concern over pollution and environmental degradation. The unprecedented turnout helped spur the creation of the EPA and landmark environmental legislation later that year.

A series of gas explosions in the sewer system of Guadalajara, Mexico, kills over 200 people.

A series of powerful explosions ripped through the sewer system beneath the streets of Guadalajara, Mexico, after gasoline leaking from a damaged pipeline accumulated in the underground tunnels, killing over 200 people and destroying several city blocks. Investigations revealed the disaster resulted from years of inadequate maintenance and warnings that had gone unheeded by officials.

More than 170 countries sign the Paris Agreement on climate change at the United Nations.

Representatives of more than 170 countries gathered at United Nations headquarters in New York to sign the Paris Agreement, a landmark international accord committing signatory nations to efforts limiting global temperature rise and reducing greenhouse gas emissions, marking the largest single-day signing of an international agreement in UN history.