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On April 20, 1999, two students at Columbine High School in Littleton, Colorado, killed 13 people and wounded 24 before taking their own lives. The Columbine Massacre was the deadliest school attack in American history up to that date. It triggered a national debate on gun control, violence in media and bullying that remains relevant more than 25 years later.

On April 20, 2010, the Deepwater Horizon oil platform exploded in the Gulf of Mexico, killing 11 workers and starting the largest oil spill in American history. For 87 days, more than 700 million litres of crude oil flowed into the sea before the well was capped. The disaster caused immense ecological damage to the coasts of five southern US states and cost BP more than $65 billion.

On April 20, 1889, Adolf Hitler was born in Braunau am Inn, Austria — who would lead Germany and the world to the greatest catastrophe in history. Leader of the Nazi Party from 1921 and Chancellor of Germany from 1933, Hitler was the architect of the Holocaust, which murdered six million Jews, and of World War II, which caused between 70 and 85 million deaths. He committed suicide in his bunker on April 30, 1945.