The first attempts to integrate concepts from complexity theory into the study of international relations (IR) and global politics began in the early 1990s. Since then, adoption of complexity approaches to explain outcomes in global politics has grown significantly, particularly in the last decade. Complexity theory (or complex systems theory) describes a range of approaches aimed at addressing the perceived shortcomings of conventional approaches for explaining the behavior of physical and social systems. Complex systems approaches highlight the nonlinear, adaptive, coevolutionary, networked, and emergent behavior of systems. Increasingly, these concepts are being applied to systems implicated in the study of global politics by scholars of IR and its related disciplines, including global governance, public policy, security studies, critical security studies, peace and conflict studies, political economy, and environmental governance. Complex systems approaches have been used to critique conventional IR theories like realism, liberal internationalism, constructivism, and critical approaches that have dominated the field since the mid-20th century. While the application of complexity science methodologies has been relatively limited (with the exception of agent-based modeling), complexity concepts like emergence and coevolution have gained traction among scholars seeking to understand the myriad factors that lead to outcomes such as peace, violence, cooperation, system destabilization, and effective policymaking. Network approaches have also been commonly used to understand systems with many actors that have dynamic and distributed power structures. Complexity is sometimes flagged as an empty “buzzword” – which is certainly the case for some of the literature that claims to apply a complex systems approach to global politics. Thus, the challenge was to focus on scholarship that engaged earnestly with complexity theory rather than to simply applying a “complexity sheen” to conventional ideas. Beginning with General Overviews, three subcategories of literature are then presented that use complex systems approaches to critique and engage with IR theory: Paradigmatic Critiques, World Order, and Topic-Specific Theoretical Critiques. The remaining sections present literature from several subfields: Security Studies; Peace and Conflict Studies; Critical Theory; Policy and Governance; Environment and Energy Governance; Political Economy, Development, and Finance; and Sociology and Interdisciplinary Social Science.
