Terrorism
Terrorist acts frequently have a political purpose. Some official, governmental definitions of terrorism use the criterion of the illegitimacy or unlawfulness of the act. to distinguish between actions authorized by a government (and thus "lawful") and those of other actors, including individuals and small groups. For example, carrying out a strategic bombing on an enemy city, which is designed to affect civilian support for a cause, would not be considered terrorism if it were authorized by a government. This criterion is inherently problematic and is not universally accepted, because: it denies the existence of state terrorism. An associated term is violent non-state actor.
Unrestricted Warfare
Another instance of threats to nations within the scope of the concept of "unrestricted warfare" is terrorism. Terrorism is used by a group to gain satisfaction for certain demands. Even if these demands are not satisfied, a terrorist attack can have vastly disproportionate effects on national welfare. One only has to look at the economic crisis that followed the terrorist attacks against the United States, or the extensive security measures put in place after those same attacks. Terrorism erodes a nation's sense of security and well being, even if the direct effects of the attacks only concern a minute percentage of the population.