THE PUZZLEWar is an extremely costly way for states to settle their disputes. Given the human and material costs of military conflict, why do states sometimes wage war rather than resolve their disputes through negotiation?
Above: States may go to war over territory that they consider integral to their nation. In 2020, Indian and Chinese soldiers clashed along the Line of Control in Ladakh, a disputed territory that lies between the two countries. The conflict resulted in 20 Indian casualties. Could tensions over the region lead to war?
In August 1914, the major countries of Europe embarked on a war the likes of which the world had never before seen. Convinced that the war would be over by Christmas, European leaders sent a generation of young men into a fight that would last four years and claim more than 15 million lives. The fighting was so intense that in one battle the British army lost 20,000 soldiers in a single day, as wave after wave of attacking infantry were cut down by German machine guns. At the time, it was called the Great War. Those who could never imagine another such horrific event dubbed it the “war to end all wars.” Today, we know this event as the First World War, or World War I, because 20 years later the countries of Europe were at it once again. World War II (1939–45) claimed 30–50 million lives.
There is no puzzle in the study of international politics more pressing and important than the question of why states go to war. It is the most tragic and costly phenomenon that we observe in social and political life. The costs of war can be counted on a number of dimensions. The most obvious cost is the loss of human life. By one estimate, wars among states in the twentieth century led to 40 million deaths directly from combat, plus tens of millions more deaths linked to war-related hardships.1 In addition, wars have left untold millions injured, displaced from their homes and countries, impoverished, and diseased.
War has economic and material costs as well. Since 2001, the United States has spent over $2 trillion on military operations in Iraq, Afghanistan, and Syria.2 Nations also routinely spend large sums of money to prepare for the possibility of war. In 2020, military expenditures by all countries amounted to just under $2 trillion—or about $250 per person.3 Wars can also disrupt the international economy. Conflicts in the oil-rich Middle East, including the Iran-Iraq War (1980–88), the Persian Gulf War (1990–91), and the Iraq War (2003–10), contributed to spikes in world oil prices. In short, as U.S. Civil War general William Sherman famously declared, “War is hell.”
But if everyone recognizes that war is hell, why do wars happen? The costs that make the puzzle of war so pressing also make the phenomenon so perplexing. Given the enormous costs associated with war, why would states sometimes choose this course?
At first glance, the answer might seem straightforward: states fight wars because they have conflicting interests over important issues. Often, for instance, two states desire the same piece of territory. Nazi Germany wanted to expand into Central Europe; World War II started when the Poles, who did not want to give up their land, fought back. In 1980, Iraq invaded Iran, in part, to seize the latter’s southern oil fields, leading to the Iran-Iraq War. Alternatively, one state might object to the policies or ideology of another. World War I grew out of Austria-Hungary’s demand that Serbia end its support for nationalist movements that threatened to tear the multiethnic Austro-Hungarian Empire apart. War between the United States and Afghanistan broke out in 2001 because the United States wanted Afghanistan to hand over Osama bin Laden and dismantle terrorist training camps on its territory, something that the Afghans refused to do. Clearly, part of the explanation for any war requires that we identify the conflicting interests that motivated the combatants.
While such interest-based explanations are correct, they are also incomplete. By identifying the object or issue over which a war was fought, they neglect the key question of why states resorted to war in order to resolve their dispute. In each case, the conflicts were disastrously costly to at least one and, in some cases, all the states involved. In addition to the millions of dead mentioned earlier, World War I led to the ouster of three of the leaders who brought their countries into the war, and it hastened the breakup of the Austro-Hungarian, Russian, and Ottoman empires. World War II brought about the defeat and occupation of its main instigators, Germany and Japan. The Nazi leader Adolf Hitler committed suicide, and his Italian ally Benito Mussolini was hung by his own people. Iran and Iraq fought for eight years only to end their conflict in a stalemate, causing 1–2 million casualties and leaving Iraq on the brink of economic collapse. The Afghan government’s refusal of U.S. demands led to its removal from power and, 10 years later, to bin Laden’s death at the hands of American soldiers. Given these grave consequences, it makes sense to wonder whether all participants would have been better off if they could have come to a settlement beforehand that allowed them to avoid the costs of war. Explaining war thus requires us to explain why its participants fail to reach such agreements.
Thinking Analytically about Why Wars Happen
Most disputes between states are settled without the parties resorting to war. Although wars tend to capture our attention, it is important to remember that war is an exceedingly rare phenomenon; most countries are at peace with one another most of the time. Figure 3.1 shows the number of states involved in interstate wars in each year from 1820 to 2020, expressed as a percentage of the total number of states in existence at the time. As the figure indicates, war is a recurrent feature of international politics in the sense that it fluctuates in frequency but never disappears completely. Yet war is the exception rather than the rule: in most years, the percentage of states involved in war is quite low. All this peace cannot be explained by an absence of issues to fight over.
Hence, when seeking to explain war, we need to ask not only “What are these parties fighting over?” but also “Why are they fighting?”4 In terms of the framework laid out in Chapter 2, answering the first question requires us to understand how states’ interests can give rise to conflicts over things like territory, policies, and the composition or character of each other’s governments. The answer to the second question lies in the strategic interactions that determine whether or how these conflicts are resolved. As we saw in the previous chapter, the international system lacks institutions—such as legislatures, courts, or international police forces—that can resolve conflicts between states through legal, judicial, or electoral mechanisms. As a result, interstate conflicts have to be settled through bargaining. Understanding why wars occur requires us to identify the factors that sometimes prevent states from settling their conflicts through peaceful bargains that would permit them to avoid the costs of war.
FIGURE 3.1The Percentage of States Involved in Interstate War per Year, 1820–2020
Figure sources: Meredith Reid Sarkees and Frank Wayman, Resort to War: 1816–2007 (Washington, DC: CQ Press, 2010). Updated to 2020 by author.
Endnotes
Bethany Ann Lacina and Nils Petter Gleditsch, “Monitoring Trends in Global Combat: A New Dataset of Battle Deaths,” European Journal of Population 21 (2005): 145–66. Return to reference 1
Neta C. Crawford, “United States Budgetary Costs and Obligations of Post-9/11 Wars through FY2020: $6.4 Trillion,” Watson Institute for International and Public Affairs, Boston University, November 13, 2019, https://watson.brown.edu/costsofwar/figures/2019/budgetary-costs-post-911-wars-through-fy2020-64-trillion (accessed 12/16/20). The $2 trillion number in the text is military spending and does not include additional expenses associated with homeland defense against terrorism and commitments to veterans’ health care.
Diego Lopes da Silva, Nan Tian, and Alexandra Marksteiner, “Trends in World Military Expenditure, 2020,” Stockholm International Peace Research Institute, April 2021, https://www.sipri.org/publications/2021/sipri-fact-sheets/trends-world-military-expenditure-2020 (accessed 5/23/2021). Return to reference 3
The theory of war developed in this chapter relies extensively on James D. Fearon, “Rationalist Explanations for War,” International Organization 49, no. 3 (Summer 1995): 379–414. Return to reference 4
