The September 11 attacks, commonly known as 9/11, were four coordinated terrorist attacks carried out by Al-Qaeda against the United States. Two crashed into the Twin Towers, one crashed into Pentagon, and the fourth – Flight 93 – was supposed to crash into a federal building in Washington, but passengers revolted and took control, leading to a crash in Somerset County, Pennsylvania. 

Nearly 3,000 people were killed and it launched a global war on terror. As the US marks the 21st anniversary of the attacks, here’s why the terrorist organization chose this particular date. 

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The date holds significance for Al-Qaeda, due to its relationship with Islam. On September 11, 1683, the Muslim armies faced a defeat in Vienna, to the King of Poland, and it became a history-altering event. The Ottoman empire didn’t recover from this defeat and thereon it was Christians or the Western world that kept dominating Muslims. Lawrence Wright wrote about this in his Pultizer-winning work, The Looming Tower. 

“For the next three hundred years, Islam would be overshadowed by the growth of Western Christian societies”, he explained. Osama bin Laden chose the date seeing the attack on the World Trade Center as Islam’s big comeback. Since then, other hardliners have used this date too, including jihadists who stormed the U.S. compound in Benghazi, killing US ambassador Chris Stevens as well as three other Americans, the Daily Star reported. 

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There is a common misconception among many that 9/11 was selected due to its similarity with the emergency contact number in the US, 9-1-1. However, Newsweek reported two other possible reasons for choosing this date was that it comes after the Labor Day weekend, which meant most Americans and the George W Bush administration would be back in their offices, maximizing the impact of the attack. Another reason was that the planes would be relatively empty on a Tuesday, meaning there’d be lesser hostile passengers to deal with.