Game theory is a method of studying decision-making situations in which the choices of two or more individuals or groups influence one another. Game theorists refer to these situations as games and to the decision makers as players. An example of such a situation is one in which the decision of each of several countries about whether to acquire nuclear weapons is affected by the decisions of the other countries. Game theory has become important in such fields as economics, international relations, moral philosophy, political science, social psychology, and sociology. Its roots are generally traced back to the book The Theory of Games and Economic Behavior (1944), by Hungarian-born mathematician John von Neumann and Austrian economist Oskar Morgenstern.