The September 11 attacks, also commonly known as 9/11, were four coordinated attacks on the United States in 2001. Nineteen people associated with Al-Qaeda, a pan-Islamist militant group, hijacked four commercial airplanes. Hijackers crashed the first two planes into each of the Twin Towers of the World Trade Center in New York City. They crashed the third plane into the Pentagon, the headquarters of the US Department of Defense, located just outside of Washington, DC. Passengers on the fourth plane diverted the plane away from Washington, DC, where the White House or Capitol were the likely targets, and the plane crashed in rural Pennsylvania.

The attacks killed thousands of people, both passengers on the planes and people in the buildings that were targeted. The United States responded by waging a decades-long “war on terror” on various Muslim-majority nation-states. This campaign resulted in the displacement of 38 million people and the direct and indirect deaths of 4.5 million people (Mazzarino, Andrea. “What the War on Terror Has to Do With the Rise in Mass Migration.” The Nation, 2023). The war on terror has not had an official ending, but the United States stopped awarding the National Defense Service Medal for the global war at the end of 2022; operations related to the war continue.