Challenging the Grey Zone

The Changing Character of Warfare and the Application of International Law

April 3 -
 4, 2019

Co-sponsored By:

Center for Ethics and the Rule of Law – University of Pennsylvania (CERL, Penn))

The Conference

The U.S. Special Operations Command defines grey zone challenges as “competitive interactions among and within state and non-state actors that fall between the traditional war and peace duality.” In the words of Gen. Joseph Votel et. al., “[t]he Grey Zone is characterized by intense political, economic, informational, and military competition more fervent in nature than normal steady-state diplomacy, yet short of conventional war.”  If the spectrum of conflict is conceived as a line running from peaceful interstate competition on the far left to strategic nuclear exchange on the far right, grey zone conflicts fall left of center. These conflicts do not fit neatly into the current international legal framework and provide many unique challenges for holding states responsible for acts of aggression that fall short of jus ad bellum principles. 

Grey zone conflicts abound in today’s world, and they aim to avoid meeting the threshold of an armed attack that would trigger a legal conventional military response. Russia’s actions in eastern Ukraine, China’s aggression in the South China Sea, and international support on both sides in the ongoing conflict and resulting humanitarian crisis in Yemen are all examples of ongoing grey zone conflicts that require the attention of the international community. Providing structure to the grey zone, whether through the application of existing international legal regimes or a novel legal construct, would serve the interests of global stability and justice. International legal or normative frameworks would allow states to better predict when their actions are a breach of another state’s sovereignty and will equip target states and the international community with accepted proportional methods to respond to such violations.

It is imperative that the United States operate within domestic legal constraints in the grey zone. To protect the rule of law and to prevent potential executive overreach, some measure of oversight and transparency in this currently opaque domain is required. Such oversight and transparency are necessary not only with respect to our own activity in the grey zone, but also in ensuring civil liberties are not violated as we protect our own nation against grey zone attacks. With that said, any attempt to regulate grey zone operations risks overly constraining the operational freedom necessary to meet our national security objectives.

This conference will bring together experts from academia, the military, the law, the private sector, and government agencies to facilitate a dialogue on the ethical, legal, and moral questions that arise from grey zone conflicts. Conference sessions will be devoted to defining grey zone tactics within the current international legal framework, examining grey zone tactics in the cyber domain, addressing issues of attribution and accountability, and examining the future of grey zone conflicts and the application or evolution of international law. 

Attendance at the non-keynote sessions of this conference is by invitation only.



Wednesday, April 3

4:30 pm – 6:00 pm

Public Keynote Address by Lieutenant General Charles Pede

Grey Zone and Future War:  Simplifying for Success

6:00 pm – 8:30 pm Cocktail Reception & Dinner for Participants

Thursday, April 4  

8:30 am – 9:30 am Sign-In and Continental Breakfast

9:30 am – 9:45 am

Welcome Remarks – Brigadier General Patrick Huston  

9:45 am – 11:00 am
Session 1

Defining Grey Zone: Situating Grey Zone Tactics and Operations Within the International Security Landscape

Moderator: Professor Claire Finkelstein

Grey zone tactics and operations abound within the current international security landscape. Grey zone tactics flourish within current internal conflicts, conventional military engagements, and ongoing transnational conflicts between state, non-state, and hybrid-state actors. However, grey zone activities, often by other names, have also existed alongside traditional warfare for much of human history. To discuss the future of the grey zone and the continued application of international law, it is necessary to understand how grey zone activities have grown and evolved into their current form. Should existing international legal regimes that govern the use of armed force apply to the grey zone? If we define the grey zone as distinct from traditional warfare, should the international community create a new legal or normative framework to regulate this space? What international legal framework should apply to grey zone conflict, and how can the United States protect its own interests in this context? What would it take to incentivize states to come together in this regard? Is the traditional notion of reciprocity sufficient?

11:00 am – 11:30 am Break (refreshments served)

11:30 am – 12:45 pm
Session 2

Grey Zone Tactics and the Cyber Domain

Moderator: Professor George Lucas

Grey zone tactics and the operations that use them can take place across all domains of military engagement. One of the fundamental domains of grey zone operations is cyber. Cyber-centric grey zone tactics are common in all forms of grey zone operations. Cyber warfare itself, however, is not exclusive to grey zone conflict. Within the grey zone, cyber tools exist as a critical force multiplier, enabling a wide variety of other grey zone tactics to have enhanced effect. Given the differences between traditional cybersecurity concerns and the role of the cyber domain within grey zone conflict, is it necessary to approach grey zone cyberwarfare any differently than cyberwarfare within conventional conflict? When does a cyberattack become an act of war? As networks transcend national boundaries with the ability to affect non-target states, what opportunities are there for multilateral cyber-defense initiatives?  How should we conceive of a proportional response to cyberattacks that often result in unforeseeable or unintended consequences? Given UN Charter Chapter 7, Article 51’s arguably high threshold for legal self-defense and the increased use of cyberspace for grey zone operations, should the UN redefine Article 51 so that “armed attack” includes non-kinetic tactics in cyberspace like attacks on critical infrastructure? How do we apply retaliatory terms such as “preemptive,” “anticipatory,” and “preventive” in cyberspace? What is an imminent threat in cyberspace, e.g., would a sleeper virus constitute an imminent threat?

12:45 pm – 2:00 pm Lunch – Keynote Lecture by Admiral Michael Rogers

2:00 pm – 3:15 pm
Session 3

Attribution and Proxy Wars: Determining Responsibility for Grey Zone Actions

Moderator: Captain Todd Huntley 

Many grey zone tactics aim to deny an opponent’s ability to credibly attribute responsibility for grey zone operations. Without attribution, it becomes difficult for victims of grey zone tactics—or the international community at large—to assign blame and ultimately to hold an actor accountable. Because certainty in the grey zone is elusive, should we look to civil and criminal law for guidance as to an appropriate standard upon which we can weigh evidence to determine attribution? For example, should we determine attribution based on a “preponderance of the evidence” standard or a “beyond a reasonable doubt” standard? Who should ultimately determine attribution, and select and impose enforcement? Is it a bilateral issue between the offending state and the target state or should an international body be responsible for adjudicating attribution matters? If attribution cannot be determined, what effective steps can a target state take to respond geo-politically as opposed to legally, e.g., name and shame, diplomatic isolation, requesting removal from international bodies, or sanctions?    

The legal and ethical dilemmas associated with the attribution dilemma are similar to those related to proxy wars.  Third-party support for states engaged in a conventional war is perhaps the oldest grey zone tactic. In addition to providing non-kinetic grey zone support, global and regional powers as well as aligned smaller states have armed, trained, and funded armies and militias to covertly shape a war’s outcome to their advantage. What triggers accountability for foreign governments that provide grey zone support to local forces allegedly committing war crimes or engaging in terrorism? Does foreign grey zone support “internationalize” an otherwise internal conflict such that the Law of Armed Conflict (LOAC) and other relevant international legal frameworks apply? How do we account for the proliferation and diversification of private military companies (PMCs)? Is the state that hires a PMC accountable for all actions of the PMC as it carries out the attack?

3:15 pm – 3:30 pm Break

3:30 pm – 5:00pm
Session 4

Past as Prologue: International Law and the Future of Grey Zone Environments

Moderator: Mr. Michael Adams, CRD, JAGC, USN (ret.)  

The covert, ambiguous, and technologically innovative nature of grey zone tactics renders the identification and application of international law a continuous challenge.  Grey zone tactics—military, political, economic, cyber, kinetic, and non-kinetic—transcend multiple disciplines. Given such breadth, which also gives rise to definitional issues, universal regulation and enforcement remains elusive.  Should one distinct international legal regime govern the grey zone? It could be argued that we now possess a historical record of grey zone activity and responses thereto. Have norms been sufficiently established in the grey zone so as to create new international customary law in this space? Finally, the cumbersome, sluggish nature of international legal regimes begs the question of continued applicability. How do we ensure any grey zone body of law is able to keep up with the pace of societal and technological advances that are fundamental to the development of new grey zone tactics?  


CDR (ret) Michael Adams

CDR, JAGC, USN (ret), Palantir Technologies

LT Keleigh Anderson

 Naval Special Warfare Group ONE, Staff Judge Advocate


 Nathan BanksonChief, Strategic Engagements, National Security Law Division Office of the Judge Advocate General

Mr. Dani Belo

Norman Paterson School of International Affairs, Carleton

CDR Jeff. R. Bray

Deputy, Office of Maritime and International Law (CG-LMI)

Professor Mary DeRosa

Professor of Practice; Co-Director, Global Law Scholars Program 

Ms. Arlene Fickler 

Partner, Schnader Harrison Segal & Lewis LLP; CERL Executive Board

Professor Claire Finkelstein

CERL Founder & Faculty Director; Algernon Biddle Professor of Law and Professor of Philosophy, University of Pennsylvania 

Mr. Ian Fishback

University of Michigan, Department of Philosophy 

COL (ret) 

David Graham  Associate Director for Programs and a Distinguished Fellow, Center for National Security Law, University of Virginia

COL (ret) David Gray

Director for the Center for Leadership and Ethics, Virginia Military Academy

CAPT. Joseph Hoelz

JAGC, United States Navy 

CAPT. Todd Huntley

The Judge Advocate General’s Legal Center and School 

BG Patrick Huston

 Commanding General, TJAGLCS

Dr. Michael John-Hopkins

Senior Lecturer in Law, Oxford Brookes University

Mr. Phillip Lohaus

American Enterprise Institute

Professor George Lucas

US Naval Academy and Naval Postgraduate School

Professor Duncan MacIntosh

Professor and Philosophy Department Chair, Dalhousie University; CERL Executive Board

Dr. Christopher Marsh

President, Special Operations Research Association

LTC Susan McConnell 

Chair, National Security Law Department, TJAGLCS

Mr. Daniel Medina

Director of Strategic and Technical Engagements, Glasswall Solutions Inc.


(ret)  Michael MeierSpecial Assistant to the Army Judge Advocate General for Law of War Matters  

COL (ret) Mark Mitchell

Principal Deputy Assistant Secretary of Defense

Professor Jens David Ohlin

Vice Dean and Professor of Law, Cornell Law School; CERL Executive Board

LTG Charles Pede

The Judge Advocate General, United States Army

Professor Mitt Regan

McDevitt Professor of Jurisprudence, Director of the Center on the Legal Profession, and Co-Director on the Center on National Security and the Law at Georgetown University Law Center

Admiral (ret) Michael Rogers

Team 8, Fmr. US Cybercom Commander, Fmr. NSA Director 

Mr. Joseph Rutigliano

Branch Head, International and Operational Law, United States Marine Corps

Dr. Aurel Sari

Senior Lecturer, Director of Exeter Centre for International Law

Mr. Matthew Shabat

Glasswall Solutions, U.S. Strategy Manager

LT. Ryan Sylvester

United States Navy JAG Corps

Mr. Shawn Turner

Adjunct Professor, University of Pennsylvania Law School; CERL Executive Board

Mr. Christopher Welsh

CERL Executive Director

Mr. Paul Welsh

Vice President, Analytical Graphics, Inc.; CERL Executive Board

Col Philip Todd Wold

Staff Judge Advocate, United States Special Operations Command

Mr. Jules Zacher

CERL Executive Board 

Background Readings

Session 1 – Defining Grey Zone: Situating Grey Zone Tactics and Operations Within the International Security Landscape

Rosa Brooks, Rule of Law in the Gray Zone, Modern War Institute, July 2, 2018

Todd C. Huntley and Andrew Levitz, Controlling the Use of Power in the Shadows: Challenges in the Application of Jus in Bello to Clandestine and Unconventional War Activities, Harvard National Security Journal, Vol. 5 (2014)

Aurel Sari, Legal Aspects of Hybrid Warfare, Lawfare blog post, October 2, 2015 

Catherine Lotrionte, Reconsidering the Consequences for State-Sponsored Hostile Cyber Operations Under International Law, 3 The Cyber Defense Review 73 (2018) 

Michael N. Schmidt, Virtual Disenfranchisement: Cyber Election Meddling in the Grey Zones of International Law, 19 Chicago Journal of International Law 30 (2018)

General Joseph T. Votel et al., Unconventional Warfare in the Gray Zone, NDU Press (July 2016 )

Roger McDermott, Does Russia Have a Gerasimov Doctrine, Parameters 46, no. 1(Spring 2016)

Michael Waltzer, Soft War: The Ethics of Unarmed Conflict, Cambridge University Press (2017) Foreword

Lt/ Douglas Cantwell, Hybrid Warfare: Aggression and Coercion in the Gray Zone, ASIL Insights, Vol. 21, Issue 19, (2017)

Nicholas Heras, Gray Zones in the Middle East, CNAS, September 18, 2017

Robinson, Linda, Todd C. Helmus, Raphael S. Cohen, Alireza Nader, Andrew Radin, Madeline Magnuson, and Katya Migacheva, Modern Political Warfare: Current Practices and Possible Responses. Santa Monica, CA: RAND Corporation, (2018)

John Chambers, Countering Gray-zone Hybrid Threats: An Analysis of Russia’s ‘New Generation Warfare and Implications for the U.S. Army. Modern War Institute, (October 2016)

Robert R. Greene Sands “Language and Culture Note #1: On the Gray Zone and the Space Between War and Peace,” . Small Wars Journal. 

Philip Kapusta, The Gray Zone, Special Warfare Magazine, October – December 2015.

United States Special Operations Command, The Gray Zone, White Paper, (September 2015).

 Frank Hoffman, On Not-So-New-Warfare: Political Warfare vs. Hybrid Threats, War on the Rocks, (July 2014).

 Russian Hybrid Warfare and Other Dark Arts, Michael Kofman, War on the Rocks, (March 2016).

The Challenge of Operating in the Gray Zone, Special Warfare, October – December (2015)

Session 4 – Past as Prologue: International Law and the Future of Grey Zone Environments

Michael Jefferson Adams, Jus Extra Bellum: Reconstructing the Ordinary, Realistic Conditions of Peace Harvard National Security Journal (2014 )  

Hal Brands, Paradoxes of the Gray Zone, Foreign Policy Research Institute, February 5, 2016

International Security Advisory Board: Report on Gray Zone Conflict, United States Department of State

David Carment et al., Gray zone mediation in the Ukraine crisis: comparing Crimea and Donbas (forthcoming 2019)

A. V. Demin, Soft Law Concept in a Globalized World: Issues and Prospects, Law: Journal of the Higher School of Economics 49 (2018)

Lord Jopling, Countering Russia’s Hybrid Threats: An Update (NATO Parliamentary Assembly, 2018)

Mihail Naydenov, Building the Capacity Of NATO’S Eastern European Members to Fight Hybrid War, 41 Information & Security 45 (2018)

Outplayed: Regaining Strategic Initiative in the Grey Zone. United Stated Army War College Strategic Studies Institute (2016)

Michael Mazaar, Mastering the Gray Zone: Understanding a Changing Era of Conflict, United States Army War College Strategic Studies Institute (2015) p. 126-137

Contact us

For any questions regarding the conference or registration, please contact: Jennifer Cohen at

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