this chapter addresses the state of the tradition of non-use of nuclear weapons in the twenty-first century, especially in the context of the changing U.S. nuclear policy. The tradition has been under stress since the end of the Cold War, and particularly since the September 11, 2001, terrorist attacks on U.S. targets. Changes to U.S. nuclear policy have posed one of the major challenges to the tradition. Similar to the United States, other nuclear powers, in particular Russia, Britain, and France, have also expanded the role of nuclear weapons in their strategic doctrines to include the use of chemical and biological weapons by adversaries as a trigger for nuclear response.
At the global level, the stress that the tradition encounters in the early twenty-first century arises from the responses of nuclear states to two main challengers: regional powers and transnational terrorist networks such as alQaeda. The regional challengers are states in strategically pivotal regional theaters that hold revisionist ideologies or territorial ambitions. These states have been characterized by the United States as belonging to “the axis of evil” or as “rogue states,” although a less pejorative characterization maybe “new proliferators.” Iran and North Korea are the two major challengers in this regard, but Syria is also considered part of this group, given its chemical weapons program and confrontational policies in the Middle East. North Korea is believed to have acquired a few rudimentary nuclear weapons and missiles, while Iran is presumed to be making efforts at developing nuclear weapons. During the 1980s and 1990s, two other states, Iraq and Libya, were also pursuing nuclear weapons. However, a decade of UN sanctions and the inspection regime that followed the 1991 Gulf War largely destroyed Iraq's nuclear infrastructure,