The September 11 attacks transformed the first term of President George W. Bush and led to what he referred to as the war on terror. The accuracy of describing it as a "war" and its political motivations and consequences are the topic of strenuous debate. The U.S. government increased military operations, economic measures, and political pressure on groups that it accused of being terrorists, as well as increasing pressure on the governments and countries which were accused of sheltering them. October 2001 saw the first military action initiated by the US. Under this policy, NATO invaded Afghanistan to remove the Taliban regime and capture al-Qaeda forces.

Al-Qaeda is a pan-Islamist militant organization led by Sunni Jihadists who self-identify as a vanguard spearheading a global Islamist revolution to unite the Muslim world under a supra-national Islamic caliphate. Its membership is mostly composed of Arabs, but also includes people from other ethnic groups. Al-Qaeda has mounted attacks on civilian, economic and military targets of the US and its allies; such as the 1998 US embassy bombings, the USS Cole bombing and the September 11 attacks. The organization is designated as a terrorist group by NATO, UN Security Council, the European Union, and various countries around the world.