Today we’re going to discuss the intersection of two of my favorite topics: human demographics and the laws of war. At first, you might think the two have little connection. We typically view the laws of war as an outgrowth of religious and moral concerns, neither of which are directly connected to the growth and distribution of populations. However, history reveals that the laws of war are often just a much a product of convenience and practicality as of morality, and demographics can exert a powerful pull over what a society considers just in times of war.

Iroquois Mourning Wars

The Iroquois Confederacy of North America ingrained demographic considerations in their concept of just war. Unlike many other societies around the world, the Iroquois lived in a sparsely-populated but bountiful continent. The Iroquois thus rarely fought wars over territory. Instead, if a war, natural disaster, disease, or other catastrophe killed a large proportion of a tribe, the Iroquois would embark on a “mourning war,” a kind of warfare designed to recover population. The wars involved attacking the members of rival tribes making little distinction between combatants and noncombatants. Some the Iroquois would kill, but most would be captured and brought to the stricken tribe. In time, the prisoners would become fully assimilated into the Iroquois.

European observers in North America were horrified by the mourning wars, and described the native Americans as savages who obeyed no laws of war. Yet while the Iroquois did not follow European distinctions between combatants and noncombatants, Iroquois warfare was far less bloody and destructive than that practiced across the Atlantic. As legal historian John Fabian Witt has written, Native American warfare was quite successful at preventing escalation, keeping wars small, short, and relatively bloodless.

The European settlers, on the other hand, came from a radically different demographic situation. The large population and organized armies of Europe meant a stricter difference between combatants and noncombatants, but also led to less value placed on human life in general. The two groups’ contrasting views of what constituted laws of war, coupled with broader racial and cultural differences, led to apocalyptically violent warfare in colonial North America. Neither side could understand the other’s system of wartime ethics, so in the end, no one respected any rules of warfare at all. The early conflicts between settlers and natives in north America were thus brutal wars of annihilation, combining the most destructive aspects of both the indigenous and European modes of war.

Early Islam

Sometimes, a culture’s shifting demographics can force a change in its laws of war. We can see this most clearly in the history of early Islam.

Early Muslim generals emphasized an unusually strict policy against collateral damage. The first Caliph, Abu-Bakr, instructed his soldiers: “do not cut down fruit-bearing trees; do not destroy buildings; do not slaughter a sheep or a camel except for food; do not burn or drown palm trees.” Demographic and environmental considerations played an obvious role in that principle. Coming as they did from the sparsely-populated and nomadic Arabian Peninsula, the early Muslims understood the importance of common natural resources. In fact, the relatively rules-bound nomadic way of war proved highly advantageous, as huge portions of the Near East and North Africa surrendered to the Arabs without a fight, trusting to their mercy.

However, the early Islamic way of war would not last. As the Muslims expanded and incorporated the vast populations of Iran, Egypt, and Iraq into their religion, the demographics of Islam changed. It became a settled, densely populated religion, much like the ones against which it had fought. At the same time, Muslim views on warfare began to change, following a broadly similar path to other settled civilizations in Europe and China.

The Population-Centric Laws of War

The modern laws of war, however, did not come out of sparsely populated regions like the North American frontier or the Arabian Peninsula. Rather, they evolved in densely populated, agrarian regions. The large and relatively centralized populations of China, and western Europe led to a few key innovations. By the early modern period in Europe (and far earlier in China), centralization had progressed to the level where countries could afford to pay soldiers regular salaries.

The impact of salaried soldiers development on the laws of war cannot be overstated. Previously, soldiers had lived off the land, which in practice meant robbing civilians for food and looting homes for valuables in lieu of pay. While these practices did not end with the introduction of professional, salaried troops, they changed conceptions of war. Governments and thinkers began to draw a clear line between civilians and soldiers. By the mid 18th century, the eminent lawyer Emer de Vattel was able to write broad rules forbidding soldiers to harm civilians, seize property, or do anything other than fight enemy soldiers in open and honest warfare.

However, the demographic evolution of war also led to darker developments. True, the distinction between valid and invalid target became sharper, but the highly sophisticated and industrialized nature of warfare placed ever more people on the valid target list. British blockades in the 19th and 20th centuries resulted in countless deaths from starvation. The targeting of factories, infrastructure, and the other support mechanisms of modern war ended the lives and livelihoods of far too many noncombatants. Early Islamic teachings, by contrast, had forbidden even the killing of the usafa, the camp followers who carried the weapons of supplies of soldiers, so long as they did not participate in the fighting. By the standards of modern warfare, as it has evolved over the last few centuries, usafa would have counted as an entirely legitimate target.

The 20th century was both the high and the low point of the modern, “population centric” approach to the laws of war. On one hand, we saw the codification and active enforcement of many sweeping rules intended to limit the brutality and destruction of war. Yet despite our efforts, warfare has become far uglier. In particular, the proportion of civilians who die in war has skyrocketed over the past century.

Demographics can help explain that paradox. Over the 20th century, world population exploded while (for reasons I discuss here) the size of militaries has remained stagnant or even shrunk. As cities become ever larger and more politically important, they become battlefields, with awful but predictable results for their innocent inhabitants.

The Future

That brings us to today’s world. While globalization has largely put an end to the destructive clash of radically different systems of wartime rules, worldwide demographics are changing fast. Populations are growing, aging, and urbanizing at an almost unprecedented rate. If history tells us anything, it’s that the morality and laws are war are not going to remain the same. Changing demographics alter our priorities and capacities, and as they do so, they alter the practices that we consider acceptable and unacceptable.

Perhaps population growth will place more and more civilians in harm’s way, and (I fear) diminish the value of civilians’ lives. Perhaps a shortage of young people (at least in the developed world) will cause ethicists to place a higher premium on the lives of young soldiers, despite their status as willing combatants . We rightly cherish the laws of war, but like parents, we must accept that our love does not prevent both children and principles from changing and growing over time.