Silent enim leges inter arma. With this phrase, Marcus Tullius Cicero defended the People’s tribune Milo’s killing of his adversary Clodius in 52 B.C.Footnote 1 Over time this defence has become so commonly recognised that Thomas Hobbes described it as “a fond saying, that all laws are silent in the time of war.”Footnote 2 Since it has evolved into a frequently quoted truism, it may be a Don Quixote fight against windmills to call the legitimacy of killing in war into question. It seems particularly so when considering that in the meantime warfare has been domesticated by modern humanitarian international law and opened to prosecution when crossing the threshold of a war crime. So, why shouldn’t this be sufficient to find killing in war both morally justified and sufficiently legitimised? Why cast doubt on it?
Even though killing in war is restricted and penalised to a certain degree—by outlawing the use of particularly dreadful means and terrible weapons and rejecting disproportionate effects on civilians—why is it considered permissible to kill at all? Shall the mere reason of being at war justify deadly actions? If war is given such a law-suspending power, on what ground can such a privilege be based? This question is not yet answered by simply referring to the limitations of killing in war: to the contrary, to prohibit certain acts of killing implies that otherwise these acts would be allowed. Does this mean that killing in war, unless and as long as not explicitly forbidden, is per se permitted—and thus does not require any further legitimisation? This fundamental question can easily be overlooked if killing in war, while without further ado considered lawful in principle, is scrutinised only with regards to potential restrictions. So, instead of being content with secondary issues of how killing in war may be restricted, the primary question at stake here is why and how killing in war may be legitimised in principle.
To begin, however, I must confess that, just as the mainstream literature, I too was so blinded by the perception of killing in war as a historical and anthropological phenomenon that causing death by military operations should be regarded as a matter of course. As a taboo unavoidably connected with human fatalities, war appeared as a legal vacuum in terms of permitting everything that was not explicitly prohibited. The peculiarity of this assumption can perhaps be best illustrated by comparing the radically different assessment of killing a human being inside and outside of military conflict. Whereas a “normal” homicide, unless specifically justified, is undoubtedly unlawful, killing in war is, in principle, considered lawful—without requiring an individual justification. In addition, not only is the killing of enemies in times of war per se regarded as legitimate but, the greater the death toll, the greater the military decoration. This commonly unquestioned license to kill is all the more astonishing in that, as will be shown below, no legal norm can be found that positively and explicitly declares killing in war to be lawful. Rather, it seems that this practice is based merely on militarily accepted tolerance, without having been fundamentally founded.
This tacit acceptance of killing in war as legitimate may have been tolerable as long as war, somehow declared by one state or state-like power against another, was an easily definable fight. However, in many of today’s armed conflicts, this is not the case—the face and methods of war have changed dramatically. Regarding the types and areas in which hostile conflicts may occur, in rising numbers, military activities are not confined to confrontations between states and their regular combatants but may, in a rather more asymmetric manner, be fought between soldiers and stateless combatants, internal insurgents or other terrorist groups, and transnational networks. With regards to the methods of battle, face-to-face fighting is more and more supplemented, or even substituted, by targeted killing, often performed by drones, thus turning individual confrontations into distant attacks and cyber warfare.
These and similar developments in the concept of war, though, may not be a reason for particular excitement if, in legal terms, it did not matter whether killing human beings occurred in a war or in a different, non-military conflict. This, however, is not the case. For, as stated before, whereas a “normal” homicide requires special justification for being considered lawful, killing in war is privileged, as it is principally regarded as lawful without requiring a particular justification. This fundamental difference between the “war paradigm” and a “law enforcement paradigm”Footnote 3 becomes all the more crucial, and dubious, if there is no clear borderline between murder within the “rubric of criminal law” and a deadly attack within the “rubric of war”.Footnote 4 As in the war paradigm military fighters need not fear criminal prosecution,Footnote 5 they themselves as well as the state power they are serving can feel less constrained in their actions. Therefore, it should not be a surprise that, as long as killing does not reach the threshold of a war crime in terms of international criminal law, hostile counterparts will be inclined to call an armed conflict a “war.” This explains why George W. Bush’s administration was so quick and keen to pronounce the reaction against the 9/11 terrorists and the protection against similar atrocities as the “war on terror”, thus avoiding perhaps troublesome ordinary criminal investigations or other constrictions in its means and measures.Footnote 6 However, terrorist groups combatting in a so-called “war” may for their part, too, claim the privilege of fighting in a war, and, thus become exempt from any prosecution for homicide—at least if a transnational element is involved.
In short, call an armed conflict or the prosecution and prevention of terrorist acts a “war” and you are much better off: above ordinary criminal law and less bound to respect human rights guarantees. What makes this assumption even worse is the fact that we increasingly lack clear criteria for what constitutes a war, opening the door for killing while “law falls silent”.Footnote 7 This danger is further enhanced by the fact that everybody seems to feel empowered to call the employment of military means a “war”. “What is war and what is not-war is in fact something that people decide”. Although this statement by Michael WalzerFootnote 8 seems merely to address the anthropological and historical accounts that the concept of war depends on cultural settings and the prevailing notions of a given society, it nevertheless reveals that, as a matter of political decision, it lies in the hands of power holders—be it orderly elected governments or self-appointed groups—to call an armed operation a “war.”
This apocalyptic vision is all the more frightening because writings and debates on killing in war used to be focused on enemy fighters whereas there are in fact at least four groups of people who can be affected by killing in war. The first and second groups are the fighters on the two adversary sides, not only with regard to their active roles and legitimacy as killers but also as potential victims, in respect of which it should be asked on what legal basis they can be expected, or even obliged, to sacrifice their lives. The third and fourth groups consist of civilians, again on both sides of the military conflict and increasingly more and more afflicted by modern warfare through bombings, distant drone operations, and other hardly controllable military means. As long as the killing of innocent victims on the enemy’s side does not cross the threshold to a war crime, criminal law is considered silent. As far as fatalities among one’s own population are concerned, these innocent victims, too, may ask why their right to life is considered to be suspended by the mere fact of being at war.
Without ignoring the fact that in all these areas modern international humanitarian law certainly has brought improvements, in particular by penalising and prosecuting war crimes, we are still far from having satisfactory solutions, neither on the international level of the laws of war nor on the national level of constitutional guarantees and criminal justifications and sanctions. Although I cannot here provide a complete solution, I will propose a first step. Instead of simply taking killing in war to be a matter of course, we should pose this question: why should killing in war—as long as it is not considered a war crime—be accepted rather than—as any homicide—prohibited?
With this question in mind, I will argue against the common assumption that in times of war everything that is not expressly forbidden is permitted. I would like to make clear from the outset, however, that I am not doing this in order to impair the situation of soldiers: since they are already exposed to fatal dangers, they shall not and should not be further affected by destabilisation of their legal position.Footnote 9 Far from being so unworldly as to think that killing in war should conclusively be denied all legitimacy, I rather strive for a more fundamental foundation and clearer limitations upon it. In these terms, my main addressees are not the soldiers in the field but legislators and, as their theoretical masterminds, lawyers and political philosophers. They should feel challenged to develop a more solid foundation both for the purposes of preventing abuses and excesses of apparent privileges of war, and for providing military decision makers and actors greater legal certainty. Thus, rather than dwelling on the moral level of the “just war” tradition, which has already been extensively discussed in the literature, my focus here is more on the legal privilege of killing in war—without thereby ignoring that legitimacy may have its ultimate roots in morality.
This search for legitimacy in killing in war shall be pursued in four steps: First, I will ask whether and why killing in war, as long as it does not cross the threshold to a war crime, shall stay outside the rubric of criminal law (Sect. 2). After not having found a satisfactory answer, I will then ask whether and to what degree constitutional law could provide empowerments and restrictions to killing in war (Sect. 3). As neither framework provides full answers, I shall finally examine, as a last refuge, whether permission can be found through international law (Sect. 4) with particular attention to state sovereignty (Sect. 5). Even on this level, however, killing in war has not yet found convincing legitimisation, thus leaving further challenges to be addressed (Sect. 6).