The changing shape of the international system in the post-Cold War era has demanded that theorists and practitioners re-evaluate the nature of security in the analysis of International Relations in the modern world. While realist conceptions of security are still pivotal in determining the actions of states, the increasing prevalence of transnational threats and security interdependence has facilitated the rise of regionally coherent subsystems within which the pursuit of security cannot be achieved in the absence of cooperation. Despite modern advancements in technology and transportation, the reality remains that security threats have a higher capability to travel over short distances rather than long, and the capacity of most states to project power beyond their own regional sphere is relatively limited. Consequently, the interplay between geography and anarchy in the current international system has facilitated the rise of regional security complexes (RSCs), whereby geographically proximate states are bound within a distinct regional dynamic; be it conflict or cooperation. The regionalist perspective has sought to emphasize that security at the regional level is autonomous and distinguishable from the dynamics of the global and domestic levels and that, whilst each regional space is unique, particular variables are comparable and highlight interactions that would not occur were it not for the existence of a RSC. The purpose of this thesis is to utilise the theoretical framework of Regional Security Complex Theory (RSCT) in order to cross-compare two different regions; Southeast Asia and the South Pacific. Southeast Asia has been widely accepted as an autonomous regional construct and experiences a web of security interdependence which ensures that the security concerns of its units cannot be analysed or resolved apart from one another. The South Pacific, by contrast, has been largely ignored in the literature on regional security and has otherwise been categorized as being unstructured and too weak in its dynamic to constitute a security complex in its own right. The objective of this thesis is to outline the variables of the essential structure of a RSC so as to ascertain whether the characterization of the South Pacific as being unstructured holds true. The additional objective of this thesis is to map and cross-compare the regional security architecture of the South Pacific to that of Southeast Asia in order to highlight and pinpoint what differences exist, what they say about the region itself, and how they may be explained.