Crowd psychology is a branch of social psychology. Ordinary people can typically gain direct power by acting collectively. Historically, because large groups of people have been able to bring about dramatic and sudden social change in a manner that bypasses established due process, they have also provoked controversy. Social scientists have developed several different theories for explaining crowd psychology, and the ways in which the psychology of the crowd differs significantly from the psychology of those individuals within it. Carl Jung coined the notion of the Collective unconscious. Other major thinkers of crowd psychology include Rene Girard, Gustave Le Bon, Wilfred Trotter, Gabriel Tarde, Sigmund Freud, Elias Canetti, Steve Reicher and Julia Constintine. At a general level, crowd psychology is concerned with the behaviour and thought processes of individual crowd members and the crowd as a whole. Given the (particularly modern) prevalence of crowd events, and the potential safety issues associated with such large gatherings of people, the topic is receiving increasing attention from agencies responsible for crowd management and also from governments.