An emergency is an extraordinary occurrence or state of affairs that poses a significant danger to public health or safety. There is no precise definition, but political thinkers and legal systems have generally treated an emergency as an extreme event that strains the limits of the established legal and political order and requires the exercise of expansive and perhaps unprecedented governmental powers, especially by the executive. Prior to the twentieth century, the term was usually reserved for violent threats, such as foreign invasions, domestic insurrections, and civil wars. By the beginning of the twentieth century, it had been expanded to include economic crises, such as labor unrest, financial collapses, and depressions. In contemporary law and political thought, emergency has been broadened even further to include natural disasters, epidemic outbreaks, environmental catastrophes, and terrorist attacks. As the category has been enlarged to include new (or newly recognized) dangers, the range of powers that the government uses to address these dangers has also been expanded. Questions about the legitimacy and the legality of responses to emergency have generally dominated political and legal thought on this subject.
