hard for them to fight.
Yet many scholarly commentators and government officials still tend to view the laws of war in quite formalistic ways. They rely on textual provisions of AP I, U.N. resolutions, and even dicta found in ICJ rulings and advisory opinions. From a fabric of words, they stitch together a protective suit that will supposedly protect us from foreign attacks (now unlawful, so our enemies cannot penetrate our rhetorical armor) and against foreign condemnation (because we wear the protective armor of “law”). But this pick-and-choose approach cannot work when confronted by new circumstances. In the past few years, for example, major academic publishers have produced several books on the legal limits of cyber war.31 Scholars have published dozens of long, scholarly articles on this subject.32 As these works acknowledge, however, the world has never seen anything that could rightly be described as “cyber war.” These works cannot describe the actual practice of states, which can then coalesce into “customary law,” because no practice yet exists.
Instead, these commentators and officials simply imagine the way that existing rules might apply to new technologies. They have little of substance to work with. Scholarly studies on the laws of war, published in the second decade of the twenty-first century, are of little help. They assume that the relevant rules are those codified in AP I, before the emergence of the Internet, email, and the information revolution. Nations never reconvened to rewrite the treaty to address new technologies. These commentators believe that these rules should govern only because they are most familiar. Their views, however, will have little purchase because they do not arise from the strategic needs and military capacities that do so much to determine how nations behave in times of conflict.
We are not arguing for a world without law. It will not be easy to decide what rules should prevail or what applications would be most feasible and desirable. We are arguing for rules that respond to the circumstances of war in the twenty-first century and the opportunities presented by new technologies. To argue in this way is not radical or extreme. It is entirely traditional. The law of war as laid down in the 1970s was not the law as it was understood in the 1940s. The law of the 1940s was not the law of 1914. As law in all areas regularly does, the law of war has continually adapted to new technologies and new circumstances, when old means no longer serve necessary ends.
War, Law, and Weapons
War and law are inextricably intertwined. As mankind has discovered new technologies and developed more effective institutions, it has brought invention to war. But nations did not then develop legal codes to impose on armed conflict. Instead, their consistent behavior over time gave rise to general principles that could guide leaders and combatants in the next war. Wars come first and the law follows, rather than the other way around. Rules limited, but did not prevent, the use of force by nations to coerce other nations.
The direct relationship between innovation and war is nothing new. In the ancient world, the evolution from bronze to iron tools and the discovery of more productive means of agriculture allowed cities to deploy larger, trained armies. Economic surplus allowed states to support warriors who specialized in combat. Progress in animal breeding made possible first the chariot and then large cavalry formations. The emergence of market institutions and effective government allowed China in the East and the Romans in the West to manufacture iron weapons on a larger scale, train and deploy bigger armies, and administer larger territories.33 Whereas Sparta and its allies fielded an army in the Peloponnesian Wars of no more than 30,000,34 the Roman imperial army under Augustus reached 250,000 troops and hit a high of perhaps 450,000 under Caracalla—numbers that Europe would not see again for more than a millennium.
In the Middle Ages, advances in technology, though slow, still prompted changes in warfare. As armor improved, mounted knights supported by rural towns prevailed. A few hundred knights controlled southern Italy and Sicily; a few thousand in the First Crusade successfully invaded and held Jerusalem.35 But the invention of the crossbow in the eleventh century (along with improvements in the longbow) led to the weakening of knightly superiority in Europe; in China, where these weapons came into existence much earlier, mounted knights never held the upper hand. Progress in shipbuilding and navigation led to the replacement of human-powered triremes with wind-powered men-of-war. The invention of gunpowder made possible artillery and siege weapons, and professional militaries equipped with small arms. Military historian Victor Davis Hanson has argued that the Western nations became dominant because their innovative societies, capitalist and proto-democratic at the beginning of the modern world, more quickly adapted and deployed new technologies to war.36
Nevertheless, the relatively slow development of human societies kept military affairs relatively static. Despite the evolution of weaponry from the ancient and medieval worlds to the Renaissance, tactics and strategy did not significantly change. Horses still provided mobility on land and wind drove ships at sea. Armies and navies still fought at close quarters within eyesight of each other. Generals could move their forces only short distances because of the limits of transportation technology and logistics. Firearms and artillery increased the casualties in these confrontations, but not their distance or speed. Alexander the Great would have recognized the formations, tactics, and strategies of Napoleon Bonaparte or even Robert E. Lee.
As military technology evolved at this slow pace, the rules of warfare did not change much. In the ancient world, law imposed few limits on combat, and those that prevailed seemed to hinge more on fidelity to the gods, rather than to man. It is not recorded whether the victims of the first iron weapons or the first war chariots demanded an international convention to outlaw their use. But if there were demands for a ban on such weapons, they did not succeed. In medieval times, there were repeated efforts to ban the crossbow. Pope Urban II, better known for urging knights to embark on the First Crusade, also urged the repudiation of this weapon. A Byzantine princess denounced it as “a truly diabolical machine.” A few decades later in 1139, the Second Lateran Council urged a formal ban. The Holy Roman Emperor Conrad III decreed that use of the weapon should be punished as a capital crime.37
These protestations went unheeded because the law could not prevent armies from seizing the battlefield advantages offered by these new weapons. In a world where mounted nobles were the decisive military force, the crossbow was a disruptive weapon. It could launch arrows with sufficient force to burst through armor. It threatened to displace the lifelong training and valor of knights and nobles with a devastating mechanism, typically wielded by artisans or peasants (who were otherwise prohibited from carrying arms). The ban failed simply because the crossbow proved too valuable in winning battles.38 With the right training, companies equipped with the longbow—a weapon already mentioned in the Bible—could devastate mounted nobles, as English kings and their well-trained peasants proved repeatedly in the Hundred Years War. Efforts to ban the longbow also failed; so too with the arquebus, forerunner of the musket, which appeared in the sixteenth century.39 Some commanders treated wielders of this new weapon as, in effect, war criminals who should be killed at once.40 But advanced nations would not stop deploying soldiers trained to use the new weapons because they so effectively altered the balance of power in their favor. Too many commanders insisted on retaining the advantages offered by these new weapons.
War’s nature only began to shift significantly with the profound economic changes that occurred in the nineteenth century. Before the Industrial Revolution, mankind made no significant gains in productivity. The distribution of wealth in the world depended more on the size of a nation’s population. In 1000, for example, Western European GDP was $11 billion (in 1990 dollars), in 1500 it had risen to only $44 billion (less than doubling every century), and in 1700 it reached $81 billion. But the Industrial Revolution and the emergence of market capitalism in the nineteenth century broke humanity out of this Malthusian trap. Advances in agricultural and industrial productivity, due to technology, management, and political and legal systems, allowed for stunning increases in wealth and economic growth. In 1870, Western European GDP, estimated at $11 billion in 1500 (in 1990 dollars), exploded to $367 billion by 1870 and $840 billion by 1913.41 The United States grew even faster. Its economy started at only $527 million in 1700. By 1870, the U.S. economy had reached $98 billion, and in 1913 it quintupled to $500 billion. China’s economy, which did not experience a nineteenth-century Industrial Revolution, actually shrunk for most of