Complexity theory arose in the natural sciences as a response to the fact that the behavior of many systems cannot be wholly explained by reference to their component parts, for example an ant colony appears vastly more complex than an ant. Complexity theory demonstrates that much of the order in such systems has arisen not from centralized control, nor from individual purpose, but from a natural, unplanned, self-organizing behavior that emerges as the components interact.
Its areas of application range from risk assessment to the modeling of consumer behavior. The influence of complexity science is increasing in the areas of security, intelligence, nuclear proliferation research, and modeling and understanding terrorist networks. Complexity methods may be used to assess opportunities, risks, contingencies, and low-probability, high-impact "black swan" events. Complexity principles in combination with scenario planning have been used to build on our understanding of leadership practice and decision-making processes to create new approaches in conflict resolution and resource management.