The project recognises that Grey Zone Warfare is far from a recent development in conflict, and we argue the perceived dichotomy between “past” and the “present” dominant forms of warfare is a deeply flawed basis for our understanding. The guerrilla during the Peninsular War of the early 19th century, the ‘petites guerres’ that accompanied early modern sieges and the Ottoman Empire’s employment of Barbary Pirates to harass shipping of states it was formally at peace with, can all be characterised as Grey Zone Warfare. Analysis of historic experiences will contribute to future-proofing and enriching debates and policies on the pressing issue of Grey Zone Warfare.

Network Members

Associate Professor TSE Wai Kit Wicky, Associate Professor, Chinese University of Hong Kong

Professor David Parrott, Professor of Early Modern History, New College Oxford

Dr Bruno Cardoso Reis, Researcher, Centre of Religious History Studies, Universidade Catolica Portugesa

Professor Gunhild Hoogensen Gjørv, Professor in Critical Peace and Conflict Studies (Security and Geopolitics) and Arctic 5 Chair in Security Studies, UiT The Arctic University of Norway

Professor Sir Hew Strachan, Bishop Wardlaw Professor, University of St Andrews

Professor Donald Stoker, The Eisenhower School for National Security and Resource Strategy

Professor Wim Klinkert, Chair in co-operation with the Netherlands Defence Academy, University of Amsterdam

Dr Collin Koh Swee Lean, Research Fellow, S. Rajaratnam School of International Studies, Singapore

Professor Lise Morje Howard, Professor, Government and SFS, Georgetown University

Dr Lukas Milevski, Assistant Professor, University of Leiden

Dr Chiara Libiseller, Lecturer, University of Leiden

Dr Christophe Paulussen, Senior Researcher & Associate Fellow Rule of Law Responses to Terrorism International Centre for Counter-Terrorism, Asser Institute

Dr Brianna Rosen, Visiting Fellow of Practice, Blavatnik School of Government, University of Oxford

Dr Huw Bennett, Reader in International Relations, Cardiff University

Dr Aleksandra Pomiecko, Lecturer in Modern Russian History, University of St Andrews

Dr Jenny Benham, Reader in Medieval History, Cardiff University

Associate Members

Dr Sarah White, Lecturer in Medieval History, Lancaster University

Professor Isabelle Duijvesteijn, Professor of International Studies and Global History, University of Leiden

A central finding is that the grey zone is inherently fluid, impossible to fix in clear legal, spatial, or temporal terms. Rather than a tightly defined category, it is best understood as an ideational space between war and peace—a space that states and non-state actors exploit to pursue strategic objectives without triggering open conflict. The report also warns against what it calls “defence orientalism”, noting that Western governments frequently portray grey zone activity as something others do, even though Western powers have long operated in similar ways themselves.

Other key insights include:

• Purpose and strategic value: Grey zone methods allow states to alter or preserve the status quo, gain advantage, or avoid undesirable escalation—even when they have the capability to wage war.
• Actors beyond the military: Civilians, proxies, private military companies, and informal networks play decisive roles, often blurring the boundaries between combatant and non-combatant.
• Whole-of-society vulnerability and resilience: Disinformation, sabotage, and societal pressure points make the civilian sphere central to both threat and defence.
• Continuity over time: While technologies evolve, the fundamental nature of sub-threshold rivalry remains strikingly consistent.
• Conventional forces still matter: Deterrence and escalation control require credible military capabilities—grey zone competition cannot replace them.

The report concludes with practical implications for policymakers, including the need to distinguish clearly between grey zone activity and hybrid warfare; invest in societal resilience and strategic communication; understand how legal ambiguity shapes competition; and develop flexible frameworks that account for the shifting thresholds of contemporary rivalries.