Religion is the biggest absent of International Relations’ science. From the official formation start of this science in the West as a single academic field of studying, religion and religious studies have been forgotten by most of scholars, as far as it can be known that international relations is the most religion separated branch of social modernized sciences. Knowing about the reason of this long time and controversial absence, usually it is citing to five reasons which are the requirements of the modernization’s process in western societies, an inclusive consolidation and acceptance of religion separation principle (secularism), the Westphalia Order of the International System, the domination of the ultra-theory of rationalism on this study field, and the materialistic nature of the mainstream theories in international relations. The current article is trying to study all these reasons, and disproof them, and to claim that deleting the religion from the science of international relations does not have a rational excuse and credibility because of the discredit of the loyalty for modernization single line process, the outbreak of serious doubts about the correctness of religion separation principle and the start of post-secularism, the start of Westphalia order’s deterioration and entering the international system into post-Westphalia era, the sunset of the ultra-theory of rationalism’s domination with the appearance of competitor ultra-theories, and also the formation of various theories and the decrease of the monopoly of the mainstream. Therefore, it is necessary to have a deep understanding of international relations by knowing about the position of religion.
