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HeinzeandNielsen-LimitedForceandtheReturnofReprisals.pdf
ROUNDTABLE: THE ETHICS OF LIMITED STRIKES
Limited Force and the Return of Reprisals in the Law of Armed Conflict Eric A. Heinze and Rhiannon Neilsen
I t is widely acknowledged that armed reprisals—the limited use of military
force by a state in response to a prior illegal action perpetrated against
that state—were formally banned by the UN Charter in . Despite
this, states have routinely engaged in the practice and continue to do so today,
often with little opposition from the international community. On April ,
, for example, the United States, the United Kingdom, and France launched
more than one hundred missiles at Syrian chemical weapons facilities in response
to the use of chemical weapons by Bashar al-Assad’s regime against civilians in the
city of Douma. While these airstrikes are more appropriately characterized as
“third-party reprisals,” since those undertaking the reprisals were not the actual
victims of the wrongful actions in question, it is noteworthy that only a very
small minority of the over seventy states that expressed a view claimed that
these strikes violated international law (including, unsurprisingly, Syria, Iran,
and Russia). Likewise, on February , , India undertook airstrikes against
a terrorist training camp located in Pakistan in reprisal for a suicide attack that
killed approximately forty Indian soldiers in Indian-administered Kashmir almost
a week earlier. Beyond increased tensions and calls for restraint, this, too, gar-
nered little international condemnation.
The advent and proliferation of cyber capabilities has arguably created further
incentive for reprisals, as state and nonstate actors acquire the ability to undertake
cyber operations that, legally speaking, may rise to the level of a use of force or
even an “armed attack,” which would give rise to the right of self-defense under
Ethics & International Affairs, , no. (), pp. –. © The Author(s), . Published by Cambridge University Press on behalf of the Carnegie Council for Ethics in International Affairs doi:./S
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Article of the UN Charter. Indeed, on May , , the Israeli Defense Forces
destroyed a building in which they alleged Hamas was poised to launch cyberat-
tacks on Israel—therein constituting the first time that a state has conducted a
kinetic military operation directly in response to an imminent malicious cyber
operation. This illustrates what might be called “cross domain reprisals,” whereby
an actor resorts to the use of kinetic force in a reprisal against a hostile cyber oper-
ation, or vice versa. Such a cross-domain reprisal was again demonstrated by the
United States in response to Iran downing a U.S. surveillance drone and alleged
attacks on oil tankers near the Strait of Hormuz on June , . In this case, the
United States opted to conduct cyber operations aimed at disabling Iranian intelli-
gence facilities and missile launch systems, precisely because such operations were
intended to fall below what would constitute an armed attack. Lastly, and most
recently, on January , , the United States killed top Iranian general Qasem
Soleimani, as well as nine other Tehran-backed militia officials, at Baghdad
International Airport via a drone strike. While the legality of the strike is still
being debated, the immediate international response from states and the United
Nations has largely been one of alarm, with fears that the “assassination of
Soleimani could ignite serious escalation in the region and possibly lead to war.”
The purpose of this essay is to examine the international law of reprisals in light of
these and other instances of states resorting to military measures short of war more
generally, paying particular attention to recent developments in the rules governing
hostile cyber operations. The first section examines reprisals in international lawand
suggests that the ban on reprisals was perhaps never as absolute as some believe. The
next section examines the developments in the rules of hostile cyber operations and
recent trends in state practice, and suggests that these may be further weakening the
ban on reprisals. We conclude with a discussion of the dangers that eroding this ban
may present, especially in an era of increasing weaponization of cyber capabilities.
The Ban on Reprisals
The contemporary doctrine of armed reprisals has its origins in the ancient practice
of “private reprisals.” During the Middle Ages, private individuals were empowered
by “letters of marque and reprisal” to undertake acts of self-help against foreign
states or their citizens as a means to recover damages incurred by some wrongful
act perpetrated by those parties. By the end of the seventeenth century, with
the increasing role of the state and the rise of state responsibility, private reprisals
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were generally tolerated less, while public reprisals emerged as an important means
of self-help, short of war, for states to address and deter wrongful acts conducted
against them. Further, throughout the eighteenth and nineteenth centuries, since
the right of states to use force was generally understood to be fairly unlimited, it
was thought that the right to armed reprisals was also unlimited. This led some
commentators to conclude that there was little basis to distinguish between war
and reprisals, as their legality was not in question—at least not until the emergence
of rules that placed limitations on the resort to force.
While the League of Nations era (–) succeeded in placing certain lim-
itations on states’ ability to resort to force, it was during this period that the first
coherent doctrine of reprisals emerged. The so-called Naulilaa Arbitration
between Portugal and Germany, which originated from a incident involving
a German reprisal against Portuguese military positions in present-day Angola, is
understood to have established the customary criteria for lawful armed reprisals of
the time. These were: () There must have been a prior violation of international
law by the target state against the claimant state; () there must have been an
attempt by the claimant state to obtain reparation or redress for the alleged
wrong by peaceful means (and such an attempt must have failed or been inappro-
priate for the circumstances); and () the force used in the reprisal must have been
proportionate to the original harm done by the target state.
Although it appears reprisals were not entirely forbidden during the League of
Nations period, the UN Charter definitively banned the practice in international
law in . Under Charter rules, states are prohibited from using force (Article
[]) unless it is either part of a UN-authorized enforcement operation or at the
invitation of the state in question, or if they are acting in self-defense against
an “armed attack” under the authority of Article of the Charter. However,
not all uses of force rise to the level of an armed attack; “only the most grave
uses of force” are grounds for invoking the right to self-defense, whereas lower-
level military actions that do not meet the “scale and severity” threshold of an
armed attack are not legal grounds for resorting to self-defensive force. So,
even if a state is the victim of the unlawful use of force, if that use of force
does not rise to the level of what is considered an armed attack, the victim
state may not respond in kind with proportionate force. Such an act would be con-
sidered an unlawful reprisal, or a “forcible countermeasure.” This interpretation of
the Charter is supported by numerous UN documents, resolutions by UN bodies,
expert opinions, and opinions of international tribunals.
limited force and the return of reprisals in the law of armed conflict 177
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However, as early as the s and s, a pattern began to emerge in the con-
ditions under which the UN Security Council was willing to condemn certain
instances of reprisals. In essence, those reprisals receiving criticism by the
Council were denounced on the basis of their disproportionality, targeting of civil-
ian assets, or the observation that they primarily served a punitive vs. deterrent
function. Scholars such as Derek Bowett observed that some reprisals were
more readily condemned by the Council during this period than others, suggest-
ing that it was not the reprisals themselves that were drawing condemnation, but
the fact that some did not meet the criteria for what members of the Council
believed was acceptable. While certainly driven by prevailing political realities
of the time, Bowett nevertheless saw international law evolving in such a way
that “reprisals remain illegal de jure, [but] become accepted de facto,” at least if
they met certain criteria.
Bowett and other skeptics of the ban on reprisals advanced their claims in the
context of a UN collective security system that had been unable to consistently and
effectively enforce a system of collective judgment and enforcement, causing states
to rely on self-help more than the framers of this system had intended. As is well
known, the UN Charter originally envisaged the right of states to use force in self-
defense under Article as a temporary measure available only to the victim state
until the collective security mechanisms of the UN could be activated, and a mul-
tilateral force could be dispatched. Relatedly, collective enforcement under
Chapter VII of the Charter was supposed to be implemented according to
Article , which commits all UN member states to make their armed forces
and military facilities available to the UN Security Council “on its call” to main-
tain international peace and security. Needless to say, this is not how the lawful
practice of self-defense occurs today. Rather, self-defense remains the purview of
states, while collective enforcement under Chapter VII relies on states voluntarily
acting on behalf of the UN. Since the Council is not able to consistently and effec-
tively enforce these elements of the collective security system, states have unsur-
prisingly resorted to self-help, including reprisals.
The International Court of Justice (ICJ) has also suggested certain qualifications
in the ban on reprisals. In the Military and Paramilitary Activities in and Against
Nicaragua case (Nicaragua v. United States of America) ()—which is often
cited as evidence in support of the ban on reprisals—the United States argued
that its use of force against Nicaragua was an act of collective self-defense primar-
ily on behalf of El Salvador, which had been attacked by insurgents who were
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supposedly armed and equipped by Nicaragua. However, the court concluded that
uses of force that do not amount to an armed attack (in this instance, Nicaragua’s
alleged assistance to Salvadorian insurgents) do not sanction collective measures
involving the use of force, but only permit nonforcible countermeasures on the
part of the victim state. In this case, therefore, the use of force by the United
States against Nicaragua on behalf of other states was illegal. The court explicitly
ruled that “States do not have a right of ‘collective’ armed response to acts which
do not constitute an ‘armed attack.’” Yet, it is not clear whether the court was
saying that the United States acted illegally because forcible reprisals are illegal,
or because the United States was not itself the victim of an unlawful act by
Nicaragua, and therefore had no right to act on behalf of the victim state.
Describing this ambiguity, Tom Ruys claims that “it is rather flabbergasting that
the Court flags a crucial potential gap in the rules on the use of force, which
would seem to be prima facie” at a disjuncture with the existing international
laws on use of force and self-defense.
The more recent Oil Platforms case (Islamic Republic of Iran v. United States of
America) (), however, leaves open the question of whether armed reprisals
may ever be lawful. In this case, the court refused to address whether the
United States acted lawfully when it attacked three Iranian oil platforms in
response to an Iranian naval mine severely damaging a U.S. Navy ship, thus miss-
ing an opportunity to settle the legal status of reprisals in international law. In a
separate opinion, Justice Bruno Simma left the door open for reprisals, interpret-
ing the ruling in Nicaragua as limiting the collective use of force, such that self-
defense may be undertaken individually or collectively, whereas reprisals may
only be undertaken by the victim state alone. He thus concluded that in response
to lower-level hostile actions, such as the naval mines deployed by Iran, states
would be entitled to undertake “proportionate countermeasures.” Simma argued
that the court in Nicaragua could not have understood this to mean “mere pacific
reprisals,” but should have rather interpreted it as “defensive military action ‘short
of’ full-scale self-defense”—that is, armed reprisals.
In short, states’ interpretation of and commitment to the illegitimacy and ille-
gality of reprisals is not as concrete as once thought. Nevertheless, the increasingly
permissive international climate pertaining to reprisals has also been facilitated by
the rules, attitudes, and activities undertaken in what is now considered to be the
fifth domain of war. Cyberspace, as a new avenue through which states and non-
state actors alike can conduct hostile operations, is influencing the return of
limited force and the return of reprisals in the law of armed conflict 179
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reprisals in a profound way, in terms of both the rules applicable to cyberspace
and the state conduct pertaining to cyber operations in recent years. At the
core of this apparent erosion are the Tallinn Manuals.
Developments in the Rules and Attitudes regarding
Hostile Cyber Operations
Responding to an increase in malicious cyber activities, the NATO Cooperative
Cyber Defence Centre of Excellence invited a group of international legal experts
(hereafter referred to as the “experts”) to shed light on how cyber operations ought
to comply with international law. The final outputs—known as the Tallinn
Manual () and Tallinn Manual . ()—are the most internationally
renowned sources on international law applicable to cyber warfare and cyber
operations, respectively. The Tallinn Manuals are not in themselves legally bind-
ing, but rather constitute “an expression of the opinion of the two International
Groups of Experts as to the state of the law.” Of course, there are also a huge
number of other excellent works that examine cyber operations in light of the
laws and ethics of armed conflict. However, the Tallinn Manuals boast the
insights of legal experts from countries around the world (including, to name a
few, Belarus, China, Israel, Thailand, and the United States), in areas ranging
from human rights law to space law, and with observers from nongovernmental
organizations such as the International Committee of the Red Cross. Given
the sheer breadth of expert insight and legal peer review in considering the law
applicable to cyberspace, the findings of the two Tallinn Manuals are thus deserv-
ing of attention.
A pillar of both of the Tallinn Manuals is that, for the purposes of determining
whether an act qualifies as a “use of force” or an “armed attack,” they do not make
a distinction between a malicious cyber operation or a kinetic operation, so long as
the “scale and effects” are comparable. This is in accord with the ICJ’s under-
standing of international customary law pertaining to “any use of force, regardless
of the weapons employed.” What matters in the cyber context, according to the
Tallinn Manual ., “is not the instrument used that determines whether the use
of force threshold has been crossed, but rather . . . the consequences of the oper-
ation and its surrounding circumstances.” Therefore, if a state falls victim to a
cyber operation that qualifies as an armed attack, that state can lawfully resort
to (collective or individual, cyber or kinetic) self-defense measures pursuant to
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Article . What the Tallinn Manual . fails to make clear in any certain terms,
however, is what a state may lawfully do if it is affected by a cyberattack that falls
short of qualifying as an armed attack.
Addressing countermeasures specifically, all of the experts contributing to the
Tallinn Manual . maintain that, as per international customary law, countermea-
sures (cyber or otherwise) must not rise to the level of an armed attack. However,
the experts then become divided over whether a countermeasure that crosses the use
of force threshold, but does not reach the level of an armed attack, would be consid-
ered lawful. Most of the experts purportedly reaffirmed the conventional view that
the “injuredstate” is not permitted to respond to thewrongful actperpetrated against
it with a use of force. The victim state would be entitled to impose countermeasures
against the offending state in such a way that suspends its legal obligations to that
state, but only to the end of inducing the offending state to re-comply with its
legal obligations. Under no circumstances, according to the conventional view,
is the injured state permitted to resort to even a proportionate use of force. As
such, most of the experts writing for the Tallinn Manual . maintain that there is
an obligation on the part of the injured state to refrain from using “forcible
countermeasures,” cyber or otherwise. The Tallinn Manual . explicitly notes that
this view thereby replicates Article () of the Articles on State Responsibility
and maintains the jurisprudence of the International Court of Justice.
A small number of the Tallinn Manual experts, on the other hand, adopt the view
that an injured state could resort to “forcible countermeasures,” cyber or otherwise,
in response to a wrongful use of force, so long as those forcible countermeasures sat-
isfy attendant international legal obligations. According to the Tallinn Manual
., the experts’ reasoning was hinged on the logic that an injured state would be
otherwise denied of a proportionate response by being restricted to measures that
necessarily fall below the use of force. Indeed, these experts (who, again, represent
only a minority) took their lead from Justice Simma’s separate opinion pertaining to
the Oil Platforms case, and explicitly cited this as influencing their view.
As a consequence of this disagreement and division, the Tallinn Manual .
provides “no such limitation”—that is, the obligation of injured states to refrain
from using forcible countermeasures—in its rules on countermeasures.
Whereas existing international law holds fast on the view that countermeasures
must not entail the use of force, recent developments in the view of international
law applicable to cyberspace leave this open for debate. In other words, because
the experts failed to agree, the Tallinn Manual . does not explicitly outline
limited force and the return of reprisals in the law of armed conflict 181
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whether a forcible countermeasure, cyber or otherwise, in response to an initial
use of force, would be considered unlawful. By deciding to refrain from including
such a limitation, the Tallinn Manual . thus fails to clearly rearticulate and
recommit to a hard ban on countermeasures that rise to the level of a use of
force—in other words, the ban on reprisals.
This point of contention is particularly concerning because, by the experts’ own
reasoning, there is no distinction between cyber or kinetic operations, as long as
the scale and severity are commensurate to the extent to which the act can be
regarded as a “use of force” or an “armed attack.” As such, states might feel at lib-
erty to interpret the Tallinn Manual .’s leniency as permitting both cyber and
noncyber forcible countermeasures in response to both cyber and noncyber uses
of force. This problematically paves the way for states to respond to cyber uses
of force with traditional kinetic uses of force.
An example of this, noted earlier, is the decision by the Israel Defense Forces
(IDF) to airstrike a building where a Hamas cyber operation was allegedly under-
way. In May , the IDF’s official Twitter account tweeted, “CLEARED FOR
RELEASE: We thwarted an attempted Hamas cyber offensive against Israeli tar-
gets. Following our successful cyber defensive operation, we targeted a building
where the Hamas cyber operatives work. HamasCyberHQ.exe has been
removed.” This, admittedly, is a different species of reprisal, since it took
place in the context of ongoing hostilities between Israel and Hamas (in other
words, a “belligerent reprisal”), and it sought to thwart a suspected cyber opera-
tion, thus potentially qualifying as an anticipatory reprisal. Nevertheless, it high-
lights the problematic potential for states to resort to force in response to even a
suspected cyberattack. The softening on the view of forcible countermeasures
prompted by the Tallinn Manual . is therefore troubling. If states believe that
they are permitted to resort to forcible countermeasures (at least insofar that
their actions will fail to elicit widespread international condemnation), then this
is likely to continue to erode the ban on reprisals. Traditional forcible countermea-
sures are then likely to become easier to contemplate and countenance, ipso facto,
thereby risking retaliation and escalation.
Conclusion: Dangers of the Return of Reprisals
When subjected to a use of force, states have an array of pacific actions that they
may lawfully resort to under the category of countermeasures. Nothing in
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international law has overturned the obligation of states to refrain from using
force unless authorized by the UN Security Council or in self-defense under the
auspices of Article . We are not suggesting anything to the contrary. Our
point is that recent interpretations of international law, as evidenced by Justice
Simma in the Oil Platforms case and the expert opinions in the Tallinn
Manuals, as well as recent state breaches of the law (which have been met with
feeble international condemnation), highlight that the ban on reprisals is in a frag-
ile and fractured state.
Each of the cases introduced at the outset of this paper have their own respec-
tive complexities. For instance, the airstrikes by the United States, the U.K., and
France in Syria technically qualify as a “third-party reprisal” and the case is further
complicated by humanitarian considerations. India’s reprisals were against the
militant group Jaish-e-Mohammed, a nonstate actor not bound by international
law but nonetheless based in Pakistan, and Israel’s missile strike against Hamas
occurred prior to the alleged hostile cyber operation. Yet if we consider Justice
Simma’s view that proportionate countermeasures could include “defensive mili-
tary action,” and the Tallinn Manual .’s failure to include a limitation on forc-
ible countermeasures, it is conceivable that each of these reprisals could be
interpreted as permissible. This is because the mere fact that they qualify as forc-
ible countermeasures does not, according to these views, call for concern, as long
as the forcible countermeasures adhere to other legal requirements, such as pro-
portionality. Indeed, it is debatable whether Israel’s choice to conduct airstrikes
was proportionate to a suspected imminent use of cyber force; it is likewise debat-
able whether Pakistan’s decision to shoot down two Indian warplanes was propor-
tionate with India’s own reprisal against a nonstate actor. Nevertheless, the fact
that these forcible countermeasures were taken in response to a threat or use of
force is not, ostensibly, that with which Justice Simma or the Tallinn Manual
. would take issue.
The example discussed in this paper that would be most appropriately viewed as
a lawful countermeasure is the U.S. decision to employ offensive cyberspace oper-
ations against Iranian military targets on June , . The United States was
reportedly “cocked and loaded” for a missile attack against military sites in
Iran, but such a reprisal was reportedly called off by U.S. president Donald
Trump because the predicted death toll of Iranian personnel was “not propor-
tionate to shooting down an unmanned drone.” Instead, the United States chose
to launch cyberattacks against Iranian facilities precisely because—as the head of
limited force and the return of reprisals in the law of armed conflict 183
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the U.S. Cyber Command insisted—these operations are “calibrated to stay well
below the threshold of war.” However, the emerging norms governing cyber
operations, as illustrated by the experts’ opinions in the Tallinn Manual ., sug-
gest that these actions may still be considered a use of force if the cyber actions
produce results similar in “scale and effect” to a kinetic use of force. This response
is in itself concerning because it would suggest that Iran could have interpreted
malicious cyber operations conducted by the United States as a use of force. If
Iran interpreted the actions in this way, then, according to at least some of the
Tallinn Manual . experts, Iran would be permitted to engage in proportionate
forcible countermeasures, cyber or otherwise. Again, it is contentious whether
the consequences of the U.S. cyber operation could be considered to be on par
with a kinetic missile strike. But by lowering the bar for resorting to forcible coun-
termeasures in response to an initial use of force, these developments necessarily
increase the risk of retaliation and the likelihood of escalation. Such developments
are therefore dangerous because they hint at, as Shane Darcy puts it, “a reinstate-
ment of the doctrine of armed reprisals, [which] would undermine the established
rules of international law on the use of military force and facilitate unilateral resort
to force that would actually threaten international peace and security.”
As both Brunstetter’s and Pearlman’s contributions to this roundtable suggest,
there are sound moral and strategic reasons for resorting to limited strikes vs. wag-
ing actual war, insofar as we assume that a state’s intention in using a limited
strike is to try to avoid escalation. However, even if we agree that limited
force is less likely to result in escalation than actual war, applying the principle
of the “probability of escalation” in the practice of limited use of force “is plagued
by ambiguity” and raises a number of concerns. First, even if the intention of a
state is to limit escalation by opting for limited strikes, whether the situation esca-
lates is ultimately not up to that state, but rather the target state. This places a lot
of faith in an entity that is already assumed to be untrustworthy and unpredictable
to accurately interpret the limited nature of the strike as an indication of a desire
not to escalate, and to act accordingly. As Robert Jervis reflects in the context of
the limited U.S. strike that killed Soleimani: “The success of coercion depends on
the adversary’s choices. . . . Iran may choose acquiescence as the path most in its
interest, but this is indeed a choice.”
Second, we should be cautious in assuming that the absence of (immediate)
escalation is because the states involved accurately interpret the limited strike as
a mechanism intended to avoid escalation. Such an outcome could just as easily
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be a result of the power asymmetries that characterize most of the examples of
limited force examined in this roundtable, wherein the weaker party knows that
it would suffer far more if the situation escalated. In this sense, if reprisals are
back on the table as a policy option, they are seemingly a tool primarily at the dis-
posal of the powerful against the weak. It is likely that they would be more prone
to escalate in less asymmetrical disputes.
Third, and owing to this, weaker states may thus calculate that they are more
able to compete by resorting to cyber operations. But again, the deployment of
cyberattacks is replete “with multiple opportunities for misunderstandings and
miscalculations,” which could produce unforeseen effects, and result in mounting
malicious exchanges within cyberspace. Moreover, as noted above, cyber opera-
tions could reasonably be interpreted as entailing a use of force, even if states
launch them to explicitly avoid escalation. In such cases, states may then find
themselves the targets of kinetic force in reprisal or retaliation.
Not only does contemplating limited strikes as a tool for conflict settlement chip
away at the restrictions on the resort to force, it erodes the obligation that states have
to resolve their disputes peacefully and normalizes this sort of violence in interna-
tional politics. The emphasis in international politics should remain on exploring ave-
nues for peaceful recourse to tensions and acting earlier in response to humanitarian
emergencies—not lowering the bar for the resort to violence, albeit short of war.
Such developments are further troubling considering recent developments in
the use of force against nonstate actors, wherein governments and commentators
increasingly recognize that nonstate actors no longer need to be under the “effec-
tive control” of a state in order to undertake an armed attack for the purposes of
Article . As a result, states have increasingly asserted a broad right to use self-
defensive force against nonstate actors in the territory of another state, even with-
out the state’s permission if the state is “unable or unwilling” to neutralize the
threat. The United States famously asserted this right after the September ,
, terrorist attacks when it targeted al-Qaeda in the territory of Afghanistan
without the country’s permission. Since that time, numerous other states (includ-
ing Colombia, Ethiopia, India, Kenya, Russia, and Turkey) have adopted a similar
view to justify their own uses of force against hostile nonstate groups operating in
neighboring states. The various armed activities conducted against the Islamic
State in Syria in hinged on the same interpretation of the law, which was
endorsed by the UN Security Council and declared by some to be a “Grotian
moment” that created a new rule of international law. Combined with the
limited force and the return of reprisals in the law of armed conflict 185
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normalization of reprisals and the proliferation of cyber capabilities, such an inter-
pretation of international law stands to significantly increase the situations in
which states feel they have the right to target nonstate actors located in other states
with either cyber or kinetic force.
Our concern in this paper is that the weakening of the ban on reprisals, in tan-
dem with other developments pertaining to uses of cyber force and self-defense
against nonstate actors, is () leading to a permissive normative-legal environment
in which states are more likely than before to resort to uses of force over contin-
uing to pursue alternative pacific measures; and () leading to situations ripe for
escalation. Suggesting that states may resort to force in reaction to an initial unlaw-
ful use of force (cyber or otherwise) not only precariously dilutes the prohibition on
reprisals but also threatens to dissolve the distinction between Article () and
Article altogether. Indeed, the precise purpose of the gap between Article ()
and Article is to serve as a buffer against escalatory violence. An erosion of
this safeguard, facilitated by the return of reprisals, is thus a dangerous development
in light of the uncertainty involved in resorting to even limited uses of force and the
high costs of further destabilizing the international order.
NOTES
See Hans Kelsen, Principles of International Law (Clark, N.J.: Lawbook Exchange, ), p. . Michael P. Scharf, “Striking a Grotian Moment: How the Syria Airstrikes Changed International Law Relating to Humanitarian Intervention,” Chicago Journal of International Law , no. (February ), p. ; and Mary Ellen O’Connell, “The Popular but Unlawful Armed Reprisal,” Ohio Northern University Law Review , no. (), pp. –.
This then spurred a number of tit-for-tat retaliations between India and Pakistan. See “Balakot: Indian Air Strikes Target Militants in Pakistan,” BBC News, February , , www.bbc.com/news/world- asia-.
“UN Chief Urges India and Pakistan to Dial Down Tensions in Wake of Kashmir Attack,” UN News, February , , news.un.org/en/story///.
Michael N. Schmitt, ed., Tallinn Manual . on the International Law Applicable to Cyber Operations, nd ed. (Cambridge, U.K.: Cambridge University Press, ), p. .
Israel Defense Forces, “CLEARED FOR RELEASE: We thwarted an attempted Hamas cyber offensive against Israeli targets. Following our successful cyber defensive operation, we targeted a building . . . ,” Twitter, May , , twitter.com/IDF/status/.
Michael D. Shear, Eric Schmitt, Michael Crowley, and Maggie Haberman, “Strikes on Iran Approved by Trump, Then Abruptly Pulled Back,” New York Times, June , ; and Julian E. Barnes and Thomas Gibbons-Neff, “U.S. Carried Out Cyberattacks on Iran,” New York Times, June , , www.nytimes. com////us/politics/us-iran-cyber-attacks.html.
“Statement by the Department of Defense,” Defense.gov, January , , www.defense. gov/Newsroom/Releases/Release/Article//statement-by-the-department-of-defense/source/- GovDelivery/; Michael Crowley, Falih Hassan, and Eric Schmitt, “U.S. Strike in Iraq Kills Qassim Suleimani, Commander of Iranian Forces,” New York Times, January , , www.nytimes. com////world/middleeast/qassem-soleimani-iraq-iran-attack.html; and Stefan Talmon and Miriam Heipertz, “The U.S. Killing of Iranian General Qasem Soleimani: Of Wrong Trees and Red Herrings, and Why the Killing May Be Lawful after All” (Bonn Research Papers on Public International Law /, University of Bonn, Institute for Public International Law, February , ), p. .
186 Eric A. Heinze and Rhiannon Neilsen
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“World Reacts to US Killing of Iran’s Qassem Soleimani in Iraq,” Al Jazeera, January , . See also Kate Holton, “UK Says U.S. Is Entitled to Defend Itself Following Iraq Attack,” Reuters, January , , www.reuters.com/article/us-iraq-security-britain-wallace/uk-says-us-is-entitled-to-defend-itself-following- iraq-attack-idUSKBNZM.
Alan N. Salpeter and Jonathan C. Waller, “Armed Reprisals during Intermediacy—A New Framework for Analysis in International Law,” Villanova Law Review , no. (), p. .
Antonio Cassese, International Law (Oxford: Oxford University Press, ), p. . See James Larry Taulbee and John Anderson, “Reprisal Redux,” Case Western Reserve Journal of
International Law , no. (), pp. –. For example, the Special Committee of Jurists, established by the League of Nations to examine the
Corfu incident, concluded that reprisals “may or may not be” consistent with the Covenant of the League of Nations. The Permanent Court of International Justice also characterized reprisals as an “alleged right” in , while the Institute of International Law passed a resolution indicating that armed reprisals were restricted similarly to all recourse to war—restricted but not entirely banned. See Shane Darcy, “Retaliation and Reprisal,” in Marc Weller, ed., Oxford Handbook on the Use of Force (Oxford: Oxford University Press, ), pp. –.
O’Connell, “Popular but Unlawful Armed Reprisal,” p. ; and Darcy, “Retaliation and Reprisal,” p. . See, especially, Military and Paramilitary Activities in and Against Nicaragua (Nicaragua v. United
States of America), I.C.J. , paras. , . See United Nations General Assembly, preamble to Article ()(a); “Declaration on Principles of
International Law concerning Friendly Relations and Co-Operation among States in Accordance with the Charter of the United Nartions,” A/RES/ (XXV), October , ; J. L. Brierly, The Law of Nations: An Introduction to the International Law of Peace (New York: Oxford University Press, ), p. ; and International Court of Justice, advisory opinion, “Legality of the Threat or Use of Nuclear Weapons” (July , ), para. .
Derek Bowett, “Reprisals involving Recourse to Armed Force,” American Journal of International Law , no. (January ), p. . See also Robert W. Tucker, “Reprisals and Self-Defense: The Customary Law,” American Journal of International Law , no. (July ), pp. –.
Bowett, “Reprisals involving Recourse to Armed Force,” p. . Taulbee and Anderson, “Reprisal Redux,” pp. –; and Tucker, “Reprisals and Self-Defense,” p. . Article , Charter of the United Nations, October , . Nicar. v. U.S., para. . Ibid., para. . Tom Ruys, ‘Armed Attack’ and Article of the UN Charter Evolutions in Customary Law and Practice
(Cambridge, U.K.: Cambridge University Press, ), p. . Oil Platforms (Islamic Republic of Iran v. United States of America), I.C.J. , separate opinion of
Judge Simma, para. : “But we may also encounter a lower level of hostile military action, not reaching the threshold of an ‘armed attack’ within the meaning of Article of the UN Charter. Against such hostile acts, a State may, of course, defend itself, but only within the more limited range and quality of responses (the main difference being that possibility of collective self-defense does not arise, cf. Nicaragua) and bound to necessity, proportionality, and immediacy in time in a particular way.”
Oil Platforms, para. . The requirement for greater clarity regarding how international law applies to cyber operations became
particularly pertinent after the Russian-supported cyberattacks against the Estonian government on April , . See Toomas Hendrik Ilves, forward in Schmitt, Tallinn Manual ., pp. xxiii–xxiv.
Michael N. Schmitt, ed., Tallinn Manual on the International Law Applicable to Cyber Warfare (Cambridge, U.K.: Cambridge University Press, ); and Schmitt, Tallinn Manual ..
Schmitt, Tallinn Manual ., n., pp. –. See, for instance, Michael L. Gross and Tamar Meisels, Soft War: The Ethics of Unarmed Conflict
(Cambridge, U.K.: Cambridge University Press, ); George Lucas, Ethics and Cyber Warfare: The Quest for Responsible Security in the Age of Digital Warfare (Oxford University Press, ); and Martha Finnemore, “Ethical Dilemmas in Cyberspace,” Ethics & International Affairs , no. (Winter ), pp. –.
For a list of experts and contributors to the first Tallinn Manual, see Schmitt, Tallinn Manual on the International Law Applicable to Cyber Warfare, pp. xix–xxii; for experts and contributors to the second Tallinn Manual, see Schmitt, Tallinn Manual ., pp. xii–xviii. See also Eric Talbot Jensen, “The Tallinn Manual .: Highlights and Insights,” Georgetown Journal of International Law , p. .
Schmitt, Tallinn Manual ., p. . International Court of Justice, “Legality of the Threat or Use of Nuclear Weapons,” para. . See also
Schmitt, Tallinn Manual ., p. .
limited force and the return of reprisals in the law of armed conflict 187
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Schmitt, Tallinn Manual ., p. . Ibid., p. . In the Tallinn Manuals, “injured state” refers to the state affected by the initial unlawful use of force.
See, for instance, Schmitt, Tallinn Manual, p. , and Schmitt, Tallinn Manual ., p. . See Yoram Dinstein, War, Aggression and Self-Defence, th ed. (Cambridge, U.K.: Cambridge University
Press, ), p. . O’Connell, “Popular but Unlawful Armed Reprisal,” p. . See International Law Commission, Art. ()(a), “Draft Articles on Responsibility of States for
Internationally Wrongful Acts,” A/RES//, November , and Nicar. v. U.S., para. . Schmitt, Tallinn Manual ., p. . These countermeasures include, for instance, proportionality, discrimination, and human rights law.
See Schmitt, Tallinn Manual ., pp. –. Ibid., p. . Ibid., p. . Israel Defense Forces, “CLEARED FOR RELEASE.” In addition to countermeasures, states are also permitted to engage in acts of retorsion—that is,
unfriendly or discourteous acts that are nonetheless lawful. See Darcy, “Retaliation and Reprisal,” p. . Donald Trump, quoted in “US-Iran: Trump Says Military Was ‘Cocked and Loaded’ to Retaliate,” BBC
News, June , , www.bbc.com/news/world-us-canada-. Julian E. Barnes, “U.S. Cyberattack Hurt Iran’s Ability to Target Oil Tankers, Officials Say,” New York
Times, August , , www.nytimes.com////us/politics/us-iran-cyber-attack.html. See also Barnes and Gibbons-Neff, “US Carried Out Cyberattacks on Iran”; and Schmitt, Tallinn Manual ., pp. –.
Darcy, “Retaliation and Reprisal,” p. . Daniel R. Brunstetter, “Wading Knee-Deep Into the Rubicon: Escalation and the Morality of Limited
Strikes,” Ethics & International Affairs , no. (July, ), pp. –. Wendy Pearlman, “Syrian Views on Obama’s Red Line: The Ethical Case for Strikes against Assad,” Ethics & International Affairs , no. (July, ), pp. –.
On the principle of “probability of escalation,” see Daniel R. Brunstetter and Megan Braun, “From Jus ad Bellum to Jus ad Vim: Recalibrating Our Understanding of the Moral Use of Force,” Ethics & International Affairs , no. (February ), pp. –.
Robert Jervis, “On the Current Confrontation with Iran,” War on the Rocks, January , , warontherocks. com///on-the-current-confrontation-with-iran/.
Ibid. See also Neil C. Rowe, “The Ethics of Cyberweapons in Warfare,” International Journal of Technoethics , no. (January/March ), pp. –.
Eric A. Heinze, “The Evolution of International Law in Light of the ‘Global War on Terror,’” Review of International Studies , no. (July ), pp. –.
See Ashley Deeks, “‘Unwilling or Unable’: Toward a Normative Framework for Extra-Territorial Self-Defense,” Virginia Journal of International Law , no. (), pp. –.
Michael P. Scharf, “How the War against ISIS Changed International Law,” Case Western Reserve Journal of International Law , no. (), pp. –.
Ibid., p. .
Abstract: Armed reprisals are the limited use of military force in response to unlawful actions per- petrated against states. Historically, reprisals provided a military remedy for states that had been wronged (often violently) by another state without having to resort to all-out war in order to coun- ter or deter such wrongful actions. While reprisals are broadly believed to have been outlawed by the UN Charter, states continue to routinely undertake such self-help measures. As part of the roundtable, “The Ethics of Limited Strikes,” this essay examines the doctrine of armed reprisals in light of recent instances of states using force “short of war” in this manner. We argue that the ban on reprisals has been largely ignored by states, and that recent attempts to apply the laws of armed conflict to the cyber domain (such as the Tallinn Manual) are further weakening this prohibition. We conclude that this is a potentially dangerous development that lowers the bar for resorting to military force, risking escalation and thereby further destabilizing the interna- tional system.
Keywords: reprisals, cyber operations, Tallinn Manual, self-defense, law of armed conflict
188 Eric A. Heinze and Rhiannon Neilsen
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- Limited Force and the Return of Reprisals in the Law of Armed Conflict
- The Ban on Reprisals
- Developments in the Rules and Attitudes regarding Hostile Cyber Operations
- Conclusion: Dangers of the Return of Reprisals
