There are various theories that are employed in the study of foreign policy. These theories are the same as theories of international relations and they are discussed below:
Realism: Realism is the school of thought that explains international relations in terms of power and the exercise of power by states towards each other. Power is often defined as the ability to get another actor to do what it would not otherwise have done. The single indicator of a state’s power may be its total GDP, which combines overall size, technological level etc.
Realists believe that the international system exists in a state of anarchy a term that implies not complete chaos or absence of structure and rules, but rather the lack of a central government that can enforce rules.
On matters foreign policy, realists hold that states are the principal or most important actors in an anarchical world lacking central legitimate governance. States represent the key units of analysis. Realists also hold that the state is essentially a rational actor that makes rational decisions. Realists also believe that within the hierarchy of issues facing the state, national or international security usually tops the list.
Liberalism: Over the years liberalism has been the main contrast to realism and it continues to be to date. While realism seeks power politics in foreign policy, liberalism seeks cooperation. Liberalism also puts greater emphasis on economics as opposed to security as it holds the belief that through economic cooperation and international institutions, international security can be more easily attained and maintained.
Idealism emphasizes international law, morality, and international organizations, rather than power alone as key influences on international events. They think that human nature is basically good. They see the international system as one based on a community of states that have the potential to work together to overcome mutual problems.
Liberalists base their approach on various assumptions such as states as well as non-state, transnational actors are important entities in world politics. As opposed to structural realists with their top down view on how anarchy and the distribution of capabilities affect state behavior many Liberals take an “inside-out” view that examines how factors Liberals see economic or other forms of interdependence or interconnectedness among both state and non-state actors as tending to have if not a pacifying, then at least a moderating effect on state behavior. For liberals the agenda of international politics is extensive. The liberal rejects the notion that the agenda of international politics is dominated only by military-security issues, that also economic, social and environmental issues matter.at the state-society and individual levels of analysis affect international relations and outcomes.
Economic Structuralism (Capitalism, Marxism): this theory is a general perspective of politics or International Relations. To understand the overall economic or class structure in world in world capitalism, one must examine more than the distribution of power among states (realism), chart the movements of transnational actors and the internal political processes of states that cross national borders (liberals), or a combination of the two. Economic Structuralism focuses on the importance of economy-material factors, especially capitalist relations of dominance or exploitation-to understanding world politics. The economic-structuralist image is influenced by Marxist analyses of exploitative relations, although not all economic-structuralists are Marxists. Dependency theory is categorized here as part of the economic-structuralist image.
Social Constructivism: This is a theory of international relations that focuses more on the social identities, cultures, social structures, history and ideas and how they affect international relations. . This theory affirms that the fundamental structures of international politics are social rather than strictly material or capabilities, as neorealist theorists would have it. These social structures shape actors’ identities and interests, not just behavior. According to In the realm of foreign policy, constructivist theorists have it that foreign policy decisions are largely influenced by habits, cultures, identities and history of states. Due to the fluid nature of ideas and cultures, constructivists view the world as a project always under construction, as case of becoming as opposed to being.