國際系統的理論化是國際關係理論發展的關鍵階段之一，甚至有學者認為國際關係理論研究如同是(國際)系統理論化的傳統。國際關係學者從 1950、60 年代開始進行國際系統的理論化，嘗試建立科學研究的國際系統理論，不同的學者都嘗試藉由其他學科學者的系統理論(systems theory)提出不同的國際系統理論化途徑。國際關係歷史社會學學者歷經三階段的國際系統理論化途徑，第一階段引述歷史社會學學者的國際系統觀點，作為其國際系統理論化及批判新現實主義國際系統理論化的主張。強調國際系絡或國際系統的國家形成與發展，尤其是國際系統與國內系統之間的歷史社會關係。 其國際系統觀點是以國家系統(systems of states)而非單純的國家之間的系統(inter-national systems)為基礎。第二階段則是強調國際關係歷史社會學本身的途徑，其理論化強調國際系統及國家的歷史偶然性、結構與單元的多樣性及與系統的動態關聯性，以及結構與行為者之間的相互組成及自主性， 並且以「全球結構」與「世界社會」取代「國際系統」。近來的第三階段運用「複雜理論」(complexity theory)理論化國際系統，認為國際系統是一個鑲嵌在物理(自然、物質)系統及社會(理念)系統之內的複雜調適系統， 具有自我組織、非線性、開放及共同演化的傾向，國際系統的模式(無政府 或層級)及規律(秩序)就是從系統單元的行動而具體化。國際關係歷史社會學的國際系統理論化觀點為國際關係理論研究帶來更為多元的觀點，其國際系統理論化觀點在方法論上仍有所啟示與省思。

Theorization of the “international systems” is a critical stage in the development of International Relations Theory(IRT). Some IR scholars even thought that IRT is a tradition of(international)systems-theorization. Since the 1950s and 1960s, IR scholars began to theorize the “international systems” and build a scientific study on international systems theories. Many scholars tried to propose approaches in theorizing the “international systems” through system theories from other disciplines. Among them, the Historical Sociology of International Relations(HSIR)experienced three phases of international systems-theorization. During the first phase, scholars introduced perspectives of international systems in historical sociology to theorize international systems and criticize neorealism’s theorizing approach. It emphasized on formations and developments of states in international contexts or systems, particularly the historical-social interconnections between international systems and domestic systems. Its systems-theorization perspective is based on the “systems of states” not on “inter-national systems”. During the second phase, the systems-theorization approach of HSIR was emphasized and the focus was on the historical contingences of international systems and states, diversities of structures and units, dynamic interconnectedness of systems, and mutual constitutions and autonomies of structures and agents. It replaced “international systems” with “global structures” or “world society”. Recently, the third phase incorporated the complexity theory, that is, international systems as a complex adaptive system embedded in physical ( natural, material ) system and social (ideal)system, having characters of self-organization, nonlinear, open and co-evolution, the actions of units reified the models(anarchy or hierarchy) and regularity(order)of international systems. The international systems- theorization of HSIR not only brought in multi-perspectives for IRT, but also methodological implications on theorization of international systems.