This day marks the day that on September 11th, 2001 four passenger planes were hijacked by al-Qaeda terrorists.
American Airlines Flight 11 was hijacked by five al-Qaeda terrorists and was crashed into the North Tower of the World Trade Center.
United Airlines Flight 175 was hijacked by five al-Qaeda terrorists and was crashed into the South Tower of the World Trade Center.
American Airlines Flight 77 was hijacked by five al-Qaeda terrorists and was crashed into the Pentagon.
United Airlines Flight 93 was hijacked by four al-Qaeda terrorists and crashed into a field in Stonycreek, Pennsylvania.
Everyone on board the planes was killed.

The death toll on the ground that day in Manhattan and Washington, DC was 2,996.

The United States immediately conducted an investigation into the attacks and determined that Osama bin Laden, the al-Qaeda leader, was behind them. After Afghanistan government officials refused to comply with the United States demands to extradite Osama bin Laden, the United States invaded Afghanistan.
Osama bin Laden, after eluding attempts to capture him for years, was eventually killed in Pakistan in May of 2011.
As of July of 2018, there have been 2,372 U.S. military deaths that are a direct result of the War in Afghanistan.

9/11 is known as the worst terrorist attack in the history of the United States, surpassing the casualties of the attack on Pearl Harbor on December 7, 1941.
Since the 9/11 attack, the number of deaths from health issues related to early rescue efforts by first responders and civilian survivors has added hundreds more.
While enhanced precautionary measures have been put in place to prevent a similar catastrophe from happening again, Homeland Security officials are constantly aware that heightened vigilance can never be taken for granted.