The Global War on Terrorism (GWOT), popularly known as the war on terror, is the term that refers to an ongoing international military campaign launched by the United States government following the September 11 attacks. The targets of the campaign are primarily Islamist groups located throughout the world, with the most prominent groups being al-Qaeda, as well as the Islamic State and their various franchise groups.The naming of the campaign uses a metaphor of war to refer to a variety of actions that do not constitute a specific war as traditionally defined. 43rd President of the United States George W. Bush first used the term "war on terrorism" on 16 September 2001, and then "war on terror" a few days later in a formal speech to Congress. In the latter speech, President Bush stated, "Our enemy is a radical network of terrorists and every government that supports them." The term was originally used with a particular focus on countries associated with al-Qaeda. The term was immediately criticized by people such as Richard B. Myers, Chairman of the Joint Chiefs of Staff, and more nuanced terms subsequently came to be used by the Bush administration to publicly define the international campaign led by the United States. While it was never used as a formal designation of U.S. operations in internal government documentation, a Global War on Terrorism Service Medal was issued.

U.S. president Barack Obama, whose administration sought to avoid use of the term since taking office, announced on 23 May 2013 that the Global War on Terror was over, saying the military and intelligence agencies will not wage war against a tactic but will instead focus on a specific group of networks determined to destroy the U.S. On 28 December 2014, the Obama administration (which preferred to use the term Overseas Contingency Operation) announced the end of the combat role of the U.S.-led mission in Afghanistan; however, the U.S. continued to play a major role in the War in Afghanistan, and in 2017, U.S. President Donald Trump expanded the American military presence in Afghanistan. The rise of the Islamic State of Iraq and the Levant (ISIL) led to the global Operation Inherent Resolve, and an international campaign to destroy ISIL.

Criticism of the war on terror has focused on its morality, efficiency, and cost. According to a 2021 study conducted by the Watson Institute for International and Public Affairs, the several post-9/11 wars participated in by the United States in its war against terror have caused the displacement, conservatively calculated, of 38 million people in Afghanistan, Pakistan, Iraq, Libya, Syria, Yemen, Somalia, and the Philippines; 26.7 million people have returned home following displacement. The study estimated these wars caused the deaths of 897,000 to 929,000 people, including over 364,000 civilians, and cost $8 trillion.The notion of a "War on Terror" was contentious, with critics charging that it has been used to reduce civil liberties and infringe upon human rights, such as controversial actions by the U.S. including surveillance, torture, and extraordinary rendition, and drone strikes that resulted in the deaths of suspected terrorists as well as civilians. Many of these actions were supported by other countries, including the 54 countries that were involved with

CIA black sites, or those that helped with drone strikes. Critics accuse participating governments of using the "War on Terror" to repress minorities or sideline domestic opponents, and have criticized negative impacts to health and the environment, resulting from the "War on Terror". Critics assert that the term "war" is not appropriate in this context (much like the term "war on drugs") since terror is not an identifiable enemy and it is unlikely that international terrorism can be brought to an end by military means.