of security has been challenged by more holistic approaches to security. Among the approaches which seeks to acknowledge and address these basic threats to human safety are paradigms that include cooperative, comprehensive and collective measures, aimed to ensure security for the individual and, as a result, for the state. To enhance international security against potential threats caused by terrorism and organized crime, there have been an increase in international cooperation, resulting in transnational policing. The international police Interpol shares information across international borders and this cooperation has been greatly enhanced by the arrival of the Internet and the ability to instantly transfer documents, films and photographs worldwide. Theoretical approaches Realism Classical realism In the field of international relations, realism has long been a dominant theory, from ancient military theories and writings of Chinese and Greek thinkers, Sun Tzu and Thucydides being two of the more notable, to Hobbes, Machiavelli and Rousseau. It is the foundation of contemporary international security studies. The twentieth century classical realism is mainly derived from Edward Hallett Carr's book The Twenty Years' Crisis. The realist views anarchy and the absence of a power to regulate the interactions between states as the distinctive characteristics of international politics. Because of anarchy, or a constant state of antagonism, the international system differs from the domestic system. Realism has a variety of sub-schools whose lines of thought are based on three core assumptions: groupism, egoism, and power-centrism. According to classical realists, bad things happen because the people who make foreign policy are sometimes bad. Neorealism Beginning in the 1960s, with increasing criticism of realism, Kenneth Waltz tried to revive the traditional realist theory by translating some core realist ideas into a deductive, top-down theoretical framework that eventually came to be called neorealism. Theory of International Politics brought together and clarified many earlier realist ideas about how the features of the overall system of states affects the way states interact: "Neorealism answers questions: Why the modern states-system has persisted in the face of attempts by certain states at dominance; why war among great powers recurred over centuries; and why states often find cooperation hard. In addition, the book forwarded one more specific theory: that great-power war would tend to be more frequent in multipolarity (an international system shaped by the power of three or more major states) than bipolarity (an international system shaped by two major states, or superpowers)." The main