On the morning of 11 September 2001, 19 al-Qaeda terrorists hijacked four commercial passenger planes in the United States.
Two planes were flown into the Twin Towers of the World Trade Center in New York City, causing both towers to collapse. A third plane was crashed into the Pentagon, just outside Washington, DC. The fourth plane crashed in rural Pennsylvania after the crew and passengers attacked the terrorists on board, preventing it from hitting another target in the US capital.
These events took place in less than two hours. The attacks killed 3,000 people. The vast majority of the dead were civilians, including nationals of over 70 countries.
A few days later, US President George W Bush declared a 'War on Terror'. An invasion of Afghanistan was launched barely one month later, on 7 October 2001. American, British and Afghan United Front (Northern Alliance) forces were deployed to destroy al-Qaeda and remove the Taliban regime that had harboured the terrorist group in Afghanistan.
On 2 May 2011, the head of al-Qaeda, Osama Bin Laden, was killed by US Special Forces in Pakistan.