The increased attention paid to torture after 9/11 resulted from the persistent framing of the terrorist attacks as exceptional, signifying a new era of terrorist threat in the twenty-first century. John Yoo explains the position of the Bush administration in War by Other Means: An Insider’s Account of the War on Terror. First, he justifies the use of war rather than crime rhetoric to describe the nation’s response. In his estimation, if the 9/11 attacks had been viewed as a crime, the government would have been restricted to utilizing law enforcement and the criminal justice system to tracking down terrorists, which, he argues, would be insufficient to counter a global terrorist network like Al Qaeda. Because Al Qaeda fighters violate the laws of war by not wearing identifying uniforms and by targeting civilians, the United States is justified in claiming that the Geneva Conventions do not apply to Al Qaeda, Guantánamo, and Afghanistan, as detailed below.
Jean Elshtain makes similar contentions in Just War against Terror: The Burden of American Power in a Violent World. Elshtain considers the justifiability of the use of force generally and in the War on Terror specifically. She applies just war theory (jus ad bellum and jus in bello) to the War on Terror and the war in Iraq launched after 9/11, and finds the use of force in both instances to be warranted.
Philip Bobbitt’s Terror and Consent: The Wars for the Twenty-First Century offers perhaps the most robust theoretical understanding of the age of terror. In this masterful work, Bobbitt argues that the world has transitioned from the nation-state to the “market-state,” where the relationship between states and their citizens is increasingly similar to that of a corporation to its consumers. For Bobbitt, the issue of these wars on terror (intentionally plural) is that terrorism is the opposite of the market state: decentralized, fragmented, and not adhering to national borders. Bobbitt argues for a revamped foreign policy to combat terrorism because the law is of the utmost importance; it must be reformed, not bypassed.
Two important works that consider the implications of the war metaphor in the War on Terror are Giorgio Agamben’s State of Exception and Adam Hodges’s The ‘War on Terror’ Narrative: Discourse and Intertextuality in the Construction and Contestation of Sociopolitical Reality. Agamben’s work is referenced by many of the authors discussed in this essay. Agamben’s concept of the “state of exception” refers to the legally condoned lawlessness that arises in times of emergency, such as war. During these periods, the rule of law is suspended to supposedly protect the citizenry, and such states can become enduring aspects of government. He is concerned with the increased power of the executive branch at such times, as the ability for checks and powers to uphold the law are reduced. The War on Terror is a good example of such a state, as government officials claimed that 9/11 was unique enough to warrant an entirely new set of responses.
Hodges is interested in how the Bush administration framed its response to the terrorist attacks of 9/11, what he calls the Bush “War on Terror” narrative. He examines the use of war rhetoric to describe the country’s reaction. For Hodges, it is a discursive accomplishment that the 9/11 attacks are considered an act of war that sparked the “War on Terror.” Hodges points out that language is never neutral. Capitalization of “War on Terror” makes it a formal war. In Terrorism, Freedom, and Security, law professor Philip Heymann expresses a similar belief that the war metaphor of the War on Terror is inappropriate to use in response to 9/11, and that employing it results in the erosion of civil liberties, enabling the use of torture.
Didier Bigo and Anastassia Tsoukala have edited Terror, Insecurity and Liberty: Illiberal Practices of Liberal Regimes after 9/11, which considers how liberal democracies have gone about justifying the use of illiberal practices (including torture and surveillance) since 9/11. Because the volume primarily analyzes Europe, it is less useful for studying the US after 9/11, but provides interesting global context for the US’s War on Terror.
War by other means : an insider's account of the war on terror by 
Just war against terror : the burden of American power in a violent world by 
Terror and consent : the wars for the twenty-first century by 
The "War on terror" narrative : discourse and intertextuality in the construction and contestation of sociopolitical reality by 
Terror, insecurity and liberty : illiberal practices of liberal regimes after 9/11 by 
