Hybrid Warfare: Aggression and Coercion in the Gray Zone

Douglas Cantwell
November 29, 2017

Hybrid War as Strategy and Policy

The best way to boil a frog, the adage goes, is to turn the heat up slowly enough that the frog doesn’t realize it is being cooked. If the perpetrators hacked the stove’s software, denied their culpability, and bombarded bystanders with fake news before annexing the kitchen, one might have a workable analogy for hybrid warfare.

Alternately termed non-linear war, active measures, or conflict in “the gray zone,” hybrid warfare has no single, agreed upon definition. In the abstract, a state engaging in hybrid warfare foments instability in another state’s domestic affairs, prioritizing non-kinetic military means such as cyber and influence operations in concert with economic pressure, support for local opposition groups, disinformation, and criminal activity. It may involve the covert deployment of unmarked troops or irregular combatants, though hybrid warfare’s reliance on cyber capabilities and non-state proxies are distinctive. The strategic benefit of hybrid warfare is to obscure the involvement of an aggressor state. Even the thinnest veneer of deniability may delay or fragment opposition to actions that otherwise invite a vocal, sometimes forceful, international response.[1]

Hybrid warfare is most often associated with aggressive Russian foreign policy over the past decade. Russia’s embrace of hybrid warfare has been credited to Chief of the General Staff of the Russian military, Valery Gerasimov. In 2013, Gerasimov articulated his view of hybrid warfare as an asymmetrical response to the spread of liberal democracy in a globalized world.[2] A corollary to Clauswitz’s conception of war as politics by other means,[3] Gerasimov observed “the role of nonmilitary means of achieving political and strategic goals has grown, and, in many cases, they have exceeded the power of force of weapons in their effectiveness.”[4] Consequently, he advocated the “broad use of political, economic, informational, humanitarian, and other nonmilitary measures – applied in coordination with the protest potential of the population,” to be “supplemented by military means of a concealed character.”[5]

Observers may disagree about which cases should be classified as hybrid war. Russia’s 2008 invasion of Georgia and the resulting annexation of Abkhazia and South Ossetia, its actions in 2013 and 2014 to seize and annex Crimea, and its deployment of “little green men” leading to the declaration of the Donetsk People’s Republic in Eastern Ukraine are the clearest examples of hybrid warfare applied to full effect. However, hybrid war need not result in the annexation of territory. A disinformation campaign fomenting anti-government riots followed by a cyber-attack crippling Estonia’s digital infrastructure in 2007, orchestration of elaborate coup attempts in Macedonia in 2016 and Montenegro in 2017, support for right-wing political parties in France and Germany, and interference in the 2016 U.S. election all fit within Gerasimov’s description of hybrid warfare.[6] Rather than merely a descriptor for isolated cases or a constellation of tactics, hybrid warfare is better understood as a grand strategy aimed at destabilizing the existing liberal order.

Conceptually, framing hybrid warfare as an innovation in international affairs has drawn criticism. All states engage in some forms of covert action and non-military measures constitute essential tools of diplomacy. Additionally, hybrid warfare resembles operations undertaken by both opposing blocs during the height of the Cold War and by many modern states under the heading of irregular warfare. Skeptics have therefore questioned whether, aside from the introduction of cyber-capabilities and the name itself, there really is anything novel about hybrid war.[7] States on the front lines against the particular hybrid threat posed by Russia have answered that question in the affirmative, investing in strategic thinking on how best to counter hybrid warfare. In April 2017, a group of eleven NATO and European Union member states signed a joint Memorandum of Understanding in Finland establishing the European Centre of Excellence for Countering Hybrid Threats.[8] The Helsinki-based center, which was officially inaugurated in early October 2017, engages in strategic dialogue, research, training, and consultation to illuminate vulnerabilities to hybrid measures and improve resilience against hybrid threats.

Hybrid War Under International Law

Understanding the relationship between hybrid warfare and international law governing the use of force is central to countering hybrid threats. Hybrid measures have been employed, with increasing success, to undermine existing international protections for the territorial integrity and political independence of states. Foremost is the ban on aggressive war. Hybrid warfare has created a new vehicle for aggression, the “supreme international crime.”[9] Outlawed by the Kellogg-Briand Pact, enforced during the tribunals at Nuremberg and Tokyo, prohibited in the UN Charter, and reaffirmed in the Kampala amendments to the Rome Statute of the International Criminal Court,[10] states endorse with near unanimity the general principle that aggression violates international law.

The rub lies in attempting to define aggression and enforce its prohibition in particular cases. Incorporation of a defined crime of aggression under the jurisdiction of the International Criminal Court represents measured but uncertain progress. Aggression has not been enforced judicially since Nuremburg. States continue to disagree about the definition of aggression and powerful states that are not party to the Rome Statute—including the United States, India, China, and Russia—have not committed to the particular definition codified in the amendments. However, since entry into force of the UN Charter, states, both unilaterally and multilaterally, have acted to counter aggression. Formation of an international coalition to expel Saddam Hussein’s forces from Kuwait in 1990–91 stands as the high-water mark of marshalling collective will to forcefully counter aggression. But modern cases of aggression rarely involve a blitzkrieg of tanks and uniformed forces rolling across an international border to take a neighboring state’s capital. Few have drawn such a swift and forceful response as Operation Desert Shield and Operation Desert Storm. In cases where an act of aggression may be less immediately apparent or where the status of either the victim or aggressor state discourages a forceful response, non-forceful measures such as economic sanctions, diplomatic censure, and verbal condemnation may be employed. Such was the case following Russia’s actions in Georgia, and later in Crimea and Eastern Ukraine. That there was widespread international condemnation of Russia bolsters the general prohibition against aggression. That the international response has not resulted in a return to the status quo places Russia’s actions in Georgia and Ukraine among a handful of instances where a state has redrawn post-1945 borders with force, not simply occupying but annexing territory. As such, it is important to situate hybrid measures within the existing law they seek to circumvent.

The UN Charter prohibits aggression through its ban on uses of force done without legal justification. Article 2(4) guarantees the right of states to be free from any threat or use of force against their territorial integrity or political independence.[11] Prohibited uses of force encompass, but need not reach, the level of an armed attack, the basis for self-defense under Article 51 of the UN Charter (as well as the collective defense provision contained in Article 5 of NATO’s Atlantic Charter).[12]

Unlawful uses of force that violate Article 2(4) generally require forces engaging in military activities, whether traditional armed forces and non-state armed groups.[13] This framework has proven capable of accounting for changes in the means through which states wage war. For example, in the context of cyber operations, the Tallinn Manual, a treatise on the application of existing international law to cyberspace drafted by an international group of experts, affirms that cyber operations may constitute unlawful uses of force if they are attributed to the armed forces of a state or if their effects mimic those of traditional military operations.[14] In theory then, the UN Charter’s prohibition on the use of force is sufficient to account for hybrid threats when they resemble traditional military activities—for example when unmarked troops engage in hostilities—but also when a state employs cyber capabilities in a hybrid war campaign to damage or disable infrastructure in a way that resembles the use of bombs and bullets.

In practice, hybrid measures are designed to avoid being identified as clear violations of the Charter even when they do constitute an unlawful use of force. One way this is achieved is through an emphasis on covert action. States have long engaged in covert operations that may run afoul of Article 2(4)’s prohibition on non-intervention.[15] While reasons for engaging in covert action vary and are often mixed, uses of force may be done covertly at least in part to honor international law in the breach. Maintaining public deniability limits the establishment of opinio juris for acts that blatantly violate the Charter—important for maintaining an international system that has prevented major power war since 1945. In the context of hybrid warfare, such benevolent motivations should not be assumed. Covert means are crucial to a hybrid warfare strategy not because covert actions may discourage open violations of the Charter by others, but because it exploits the weakness of an international enforcement regime where the status quo is often inaction, particularly in those cases where aggressor states have sown doubt as to attribution or the legality of their behavior.

Other hybrid measures are simply not accounted for by the Charter’s prohibition on the use of force. For example, economic measures traditionally do not violate Article 2(4).[16] Disinformation and criminal activity generally also fall below this threshold. However, actions not constituting a use of force may still be unlawful as a form of interference. Sovereign non-interference is implicit in the doctrine of sovereign equality, enshrined in Article 2(1) of the Charter. The UN General Assembly has opined on the concept. In a 1965 declaration, the Assembly described interference as “the subordination of the exercise of [a state’s] sovereign rights” up to and including the violent overthrow of a state’s government.[17] In a 1970 declaration, the Assembly highlighted the ban on intervention in the internal or external affairs of any other state along with “all other forms of interference or attempted threats against the personality of the State or against its political, economic and cultural elements.”[18]

Interference may be understood as a lesser-included offense of intervention. The controlling expression is contained in the International Court of Justice’s (ICJ) landmark 1986 Nicaragua decision. In Nicaragua, the Court emphasized the right of all states to decide upon issues inherent to state sovereignty, to include a state’s political, economic, social and cultural system and the formulation of its foreign policy. When those choices are influenced by methods of coercion, including through subversion or indirect force, that constitutes unlawful interference.[19]

The Charter framework, therefore, is at least conceptually sufficient to address hybrid measures short of the use of force. However, since Nicaragua, the contours of what constitutes coercive interference have remained murky.[20] Lack of clarity and a threshold that has placed interference nearly on par with intervention[21] have left gaps that hybrid measures may exploit. No single element of a hybrid campaign may present a clear case of coercive interference when viewed in isolation. However, constant, coordinated interference intended to destabilize a government may violate the spirit, if not the formalistic letter, of the Charter’s protections for the political independence of states. While a state with robust civic institutions may be able to withstand a trumpet blast of false news stories, riots, and strategic leaks of information intended to undermine elections, smaller states in particular may find themselves overwhelmed. As such, it is important that coercive acts be recognized, scrutinized, and subject to a swift and coordinated response where necessary by those states and international and non-governmental institutions seeking to uphold protections on political independence enshrined in the Charter. Likewise, coercive acts must be distinguished from actions taken transparently and lawfully by states, which may exert diplomatic pressure without constituting illegal interference.


A complete understanding of hybrid war as a strategic concept requires that it be properly situated within the existing regime governing the use of force under international law. Addressing legal aspects of hybrid conflict in turn requires proper acknowledgment of hybrid campaigns that amount to aggression and more robust theorizing on what hybrid measures constitute coercive interference.[22] In that sense, efforts like the establishment of the European Centre of Excellence for Countering Hybrid Threats are a welcome development. Its supporters should ensure that the growing body of work around hybrid warfare incorporates the established lexicon of international law, an important step towards clearing the fog of war in the gray zone.

About the Author: Lieutenant, Judge Advocate General’s Corps, United States Navy. The views expressed are written solely in the author’s personal capacity and do not represent those of the U.S. Navy, the Department of Defense, or the U.S. Government.

[1] For additional background on hybrid warfare See Jen Stoltenberg, Keynote Speech by NATO Secretary General at the Opening of the NATO Transformation Seminar (Mar. 25, 2015), available at http://www.nato.int/cps/en/natohq/opinions_118435.htm; Michael Kofman, Russian Hybrid Warfare and Other Dark Arts, War on the Rocks (Mar. 11, 2016), http://warontherocks.com/2016/03/russian-hybrid-warfare-and-other-dark-arts/; Frank Hoffman, Hybrid Warfare and Challenges, Joint Force Quarterly 34–39 (2009); Aurel Sari, Legal Aspects of Hybrid Warfare, Lawfare (Oct. 2, 2015), https://lawfareblog.com/legal-aspects-hybrid-warfare.

[2] General Valery Gerasimov, The Value of Science Is in the Foresight: New Challenges Demand Rethinking the Forms and Methods of Carrying out Combat Operations, Voyenno-Promyshlennyy Kurier (original in Russian), (Feb. 26, 2013), http://vpk-news.ru/articles/14632 (last visited Nov. 27, 2017). An English version can be found at Robert Coalson (trans.), Military Review (Jan.—Feb. 2016), http://usacac.army.mil/CAC2/MilitaryReview/Archives/English/MilitaryReview_20160228_art008.pdf. For an alternate take on Gerasimov’s work, see Charles K. Bartles, Getting Gerasimov Right, Military Review (Jan.–Feb, 2016), available at http://usacac.army.mil/CAC2/MilitaryReview/Archives/English/MilitaryReview_20160228_art009.pdf.

[3] Carl von Clausewitz, On War (Michael Howard & Peter Pare trans., Oxford University Press 2007).

[4] Gersimov, supra note 2, in Coalson, supra note 2, at 24.

[5] Id.

[6] For information on the facts underlying these various examples see Max Fisher, In D.N.C. Hack, Echoes of Russia’s New Approach to Power, N.Y. Times (July 25, 2016), http://www.nytimes.com/2016/07/26/world/europe/russia-dnc-putin-strategy.html?_r=0; David E. Sanger, White House Confirms Pre-Election Warning to Russia Over Hacking, N.Y. Times (Nov. 16, 2016), http://www.nytimes.com/2016/11/17/us/politics/white-house-confirms-pre-election-warning-to-russia-over-hacking.html; Andrew Higgins, Finger Pointed at Russian in Alleged Coup Plot in Montenegro, N.Y. Times (Nov. 26, 2016), http://www.nytimes.com/2016/11/26/world/europe/finger-pointed-at-russians-in-alleged-coup-plot-in-montenegro.html.

[7] Benjamin Wittes, What is Hybrid Conflict?, Lawfare (Sept. 11, 2015), https://lawfareblog.com/what-hybrid-conflict. See also Damien Van Puyvelde, Hybrid War – Does It Even Exist?, NATO Review, http://www.nato.int/docu/review/2015/Also-in-2015/hybrid-modern-future-warfare-russia-ukraine/EN/ (last visited Nov. 27, 2017).

[8] Press Release, Government of Finland , European Centre of Excellence for Countering Hybrid Threats Established in Helsinki, (Apr. 11, 2017), http://valtioneuvosto.fi/en/article/-/asset_publisher/10616/eurooppalainen-hybridiuhkien-osaamiskeskus-perustettiin-helsinkiin; Press Release, North Atlantic Treaty Organization, NATO Welcomes Opening of European Centre for Countering Hybrid Threats, (Apr. 11, 2017), http://www.nato.int/cps/en/natohq/news_143143.htm.

[9] 22 Nuremberg Trial Proceedings, 30 Sept. 30, 1946, at 426 (The Avalon Project, 2008), available at http://avalon.law.yale.edu/imt/09-30-46.asp.

[10] See General Treaty for the Renunciation of War (Kellogg-Briand Pact), Aug. 27, 1928, 94 L.N.T.S. 57, available at http://avalon.law.yale.edu/subject_menus/kbmenu.asp; U.N. Charter; Nuremburg Trial Proceedings, supra note 9; Rome Statute of the International Criminal Court, U.N. Doc. A/CONF.183/9, July 17, 1998, available at http://legal.un.org/icc/statute/romefra.htm.

[11] U.N. Charter art. 2, ¶¶ 1, 4. See also G.A. Res. 3314 (XXIX), Definition of Aggression (Dec. 14, 1974), available at https://documents-dds-ny.un.org/doc/RESOLUTION/GEN/NR0/739/16/IMG/NR073916.pdf?OpenElement.

[12] U.N. Charter art. 51; Charter of the North Atlantic Treaty Organization art. 5.

[13] Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United States), 1986 I.C.J. Rep. 14, 202 ¶ 195 (June 27); Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda), Judgment, 2005 I.C.J. Rep.168 (Dec. 19); Legality of the Use or Threat of Nuclear Weapons, 1996 I.C.J. Rep. 226 (July 8).

[14] Tallinn Manual on the International Law Applicable to Cyber Warfare, ch. 1 (Michael N. Schmitt ed., 2013).

[15] Alexandra H. Perina, Black Holes and Open Secrets: The Impact of Covert Action on International Law, 53 Colum. J. Int’l. L. 3 (2015).

[16] Though the issue has garnered significant debate. See M. McDougal & F. Feliciano, Law and Minimum World Public Order, 3 UCLA Pac. Basin L.J. 21, 124 n.6 (1961). See also D. Bowett, International Law and Economic Coercion, 16 Va. J.Int'l L. 245, 245–49 (1976).

[17] G.A. Res. 20/2131, Declaration on the Inadmissibility of Intervention and Interference in the Domestic Affairs of States (Dec. 21, 1965), available at http://www.un-documents.net/a20r2131.htm.

[18] G.A. Res. 25/2625, Declaration on Principles of International Law Concerning Friendly Relations and Cooperation Among States in accordance with the Charter of the United Nations (Oct. 24, 1970), available at http://www.un-documents.net/a25r2625.htm.

[19] Nicar. v. U.S., 1986 I.C.J. Rep. at 202.

[20] T. J. Farer, Political and Economic Coercion in Contemporary International Law, 79 AJIL 405, 405–13 (1985).

[21] As one treatise interprets it, “the interference must be forcible or dictatorial, or otherwise coercive, in effect depriving the state intervened against of control over the matter in question.” L. Openheim, International Law 432 (9th ed. 2008). Others have interpreted this standard as a sort of cause-in-fact test whereby observers ask, but for the interference, would the impacted state have taken a particular course of action. M. Wood, Non-Intervention (Non-Interference in Domestic Affairs), The Princeton Encyclopedia of Self-Determination, http://pesd.princeton.edu/?q=node/258.

[22] For example, see Duncan Hollis, Russia and the DNC Hack: What Future for a Duty of Non-Intervention?, Opinio Juris (July 25, 2016), http://opiniojuris.org/2016/07/25/russia-and-the-dnc-hack-a-violation-of-the-duty-of-non-intervention/; Ido Kilovaty, The Democratic National Committee Hack: Information as Interference, Just Security (Aug. 1, 2016), https://www.justsecurity.org/32206/democratic-national-committee-hack-information-interference/