Before FPA analysis has developed as a discipline, it was still an area widely studied within IR. Thus, the traditional theories of IR, namely idealism and realism, also have inquiries about foreign policy. They base their explanation of foreign policy on systemic factors, that is they believe foreign policy decisions are influenced by the nature of the international system. While doing this, both idealism and realism attribute features of human nature to the states. This methodology is defined as rational-choice theory, which assumes a unified decision-making body in the form of the state, as well as a belief that the pursuit of self-interest guided all decision makers (Alden and Aran, 2017, 6). The correct answer is D.