On April 20

An explosion on Deepwater Horizon, an offshore rig in the Gulf of Mexico, resulted in the largest marine oil spill in history.

Fernando Lugo became the first candidate not from the Colorado Party candidate to be elected President of Paraguay in 61 years.

American racing driver Danica Patrick won the Indy Japan 300, becoming the first woman to win an IndyCar auto race.

An incomplete tunnel leading to the Nicoll Highway MRT station in Singapore collapsed, resulting in four deaths and the station's relocation.

Students Eric Harris and Dylan Klebold carried out a massacre at Columbine High School, killing 13 people before committing suicide.

Korean Air Lines Flight 902 was shot down after violating Soviet airspace and was forced to make an emergency landing.

Pierre Trudeau was sworn in as prime minister of Canada, succeeding Lester B. Pearson.

South African Airways Flight 228 crashed shortly after take-off from Windhoek in South West Africa, resulting in 123 deaths.

Enoch Powell (pictured), a British Conservative member of Parliament, made a controversial speech in opposition to immigration and anti-discrimination legislation, resulting in his removal from the shadow cabinet.

World War II: German and Italian forces began a large-scale counter-insurgency operation in occupied Yugoslavia.

Billie Holiday recorded the song "Strange Fruit", which later became an emblem of the civil rights movement.

Adolf Hitler's 50th birthday was celebrated as a national holiday in Nazi Germany.

A fire and a gun battle between the Colorado National Guard and striking coal miners led to 17 deaths in the Ludlow Massacre.

French explorer René Caillié reached Timbuktu in present-day Mali, and later received a 9,000-franc prize from the Société de Géographie for being the first European to return with a description of the city.

Four days after the Court of King's Bench upheld an English murder suspect's right to a trial by battle in Ashford v Thornton, the plaintiff declined to fight, allowing the defendant to go free.

War of the Fifth Coalition: Commanded by Napoleon, Franco-German forces defeated a reinforced Austrian corps at the Battle of Abensberg.

Anglo-Spanish War: The English navy sank much of a Spanish treasure fleet at the Battle of Santa Cruz de Tenerife off the Canary Islands, but was unable to capture the treasure.

Bacatá, the main settlement of the Muisca Confederation in present-day Colombia, was conquered by Spanish conquistadors led by Gonzalo Jiménez de Quesada.

Sun dogs were observed over Stockholm, Sweden, inspiring Vädersolstavlan (pictured), the oldest coloured depiction of the city.