A rivalry is the state of two people or groups engaging in a lasting competitive relationship. Rivalry is the "against each other" spirit between two competing sides. The relationship itself may also be called "a rivalry", and each participant or side a rival to the other. Someone's main rival may be called an archrival. A rivalry can be defined as "a perceptual categorizing process in which actors identify which states are sufficiently threatening competitors". In order for the rivalry to persist, rather than resulting in perpetual dominance by one side, it must be "a competitive relationship among equals". Political scientist John A. Vasquez has asserted that equality of power is a necessary component for a true rivalry to exist, but others have disputed that element.