What Happens When War Is Outlawed

What Happens When War Is Outlawed

Did a largely forgotten peace pact transform the world we live in?

Two legal scholars argue that the Paris Peace Pact of 1928—widely disparaged or ignored—led to a new international order.

Illustration by Javier Jaén

On August 27, 1928, in Paris, with due pomp and circumstance, representatives of fifteen nations signed an agreement outlawing war. The agreement was the unanticipated fruit of an attempt by the French Foreign Minister, Aristide Briand, to negotiate a bilateral treaty with the United States in which each nation would renounce the use of war as an instrument of policy toward the other. The American Secretary of State, Frank Kellogg, had been unenthusiastic about Briand’s idea. He saw no prospect of going to war with France and therefore no point in promising not to, and he suspected that the proposal was a gimmick designed to commit the United States to intervening on France’s behalf if Germany attacked it (as Germany did in 1914). After some delay and in response to public pressure, Kellogg told Briand that his idea sounded great. Who wouldn’t want to renounce war? But why not make the treaty multilateral, and have it signed by “all the principal powers of the world”? Everyone would renounce the use of war as an instrument of policy.

Kellogg figured that he had Briand outfoxed. France had mutual defense treaties with many European states, and it could hardly honor those treaties if it agreed to renounce war altogether. But the agreement was eventually worded in a way that left sufficient interpretive latitude for Briand and other statesmen to see their way clear to signing it, and the result was the General Treaty for the Renunciation of War, also known as the Paris Peace Pact or the Kellogg-Briand Pact. By 1934, sixty-three countries had joined the Pact—virtually every established nation on earth at the time.

The Treaty of Versailles, signed in 1919, gets bad press. It imposed punitive conditions on Germany after the First World War and is often blamed for the rise of Hitler. The Kellogg-Briand Pact does not get bad press. It gets no press. That’s because the treaty went into effect on July 24, 1929, after which the following occurred: Japan invaded Manchuria (1931); Italy invaded Ethiopia (1935); Japan invaded China (1937); Germany invaded Poland (1939); the Soviet Union invaded Finland (1939); Germany invaded Denmark, Norway, Belgium, the Netherlands, Luxembourg, and France and attacked Great Britain (1940); and Japan attacked the United States (1941), culminating in a global war that produced the atomic bomb and more than sixty million deaths. A piece of paper signed in Paris does not seem to have presented an obstacle to citizens of one country engaging in the organized slaughter of the citizens of other countries.

In modern political history, therefore, the Paris Peace Pact, if it is mentioned at all, usually gets a condescending tip of the hat or is dutifully registered in footnote. Even in books on the law of war, little is made of it. There is not a single reference to it in the political philosopher Michael Walzer’s “Just and Unjust Wars,” a classic work published in 1977. The summary on the U.S. State Department’s Web site is typical: “In the end, the Kellogg-Briand Pact did little to prevent World War II or any of the conflicts that followed. Its legacy remains as a statement of the idealism expressed by advocates for peace in the interwar period.”

The key term in that sentence is “idealism.” In international relations, an idealist is someone who believes that foreign policy should be based on universal principles, and that nations will agree to things like the outlawry of war because they perceive themselves as sharing a harmony of interests. War is bad for every nation; therefore, it is in the interests of all nations to renounce it.

An alternative theory is (no surprise) realism. A realist thinks that a nation’s foreign policy should be guided by a cold consideration of its own interests. To a realist, the essential condition of international politics is anarchy. There is no supreme law governing relations among sovereign states. When Germany invades France, France cannot take Germany to court. There are just a lot of nations out there, each trying to secure and, if possible, extend its own power. We don’t need to judge the morality of other nations’ behavior. We only need to ask whether the interests of our nation are affected by it. We should be concerned not with some platonic harmony of interests but with the very real balance of power.

A standard way to write the history of twentieth-century international relations is to cast as idealists figures like Woodrow Wilson, who, in 1917, entered the United States into a European war to make the world “safe for democracy,” and the other liberal internationalists who came up with the League of Nations and the Kellogg-Briand Pact. The Second World War proved these people spectacularly wrong about how nations behave, and they were superseded by the realists.

To the realists, such Wilsonian ideas as world government and the outlawry of war were quixotic. Nations should recognize that conflict is endemic to the international arena, and they should not expend blood and treasure in the name of an abstraction. Containment, the American Cold War policy of preventing the Soviet Union from expanding without otherwise intervening in its affairs, was a realist policy. Communists could run their own territories however they liked as long as they stayed inside their boxes. If our system was better, theirs would eventually implode; if theirs was better, ours would. The author of that policy, the diplomat George Kennan, called the Kellogg-Briand Pact “childish, just childish.”

And yet since 1945 nations have gone to war against other nations very few times. When they have, most of the rest of the world has regarded the war as illegitimate and, frequently, has organized to sanction or otherwise punish the aggressor. In only a handful of mostly minor cases since 1945—the Russian seizure of Crimea in 2014 being a flagrant exception—has a nation been able to hold on to territory it acquired by conquest.

Historians have suggested several reasons for this drop in the incidence of interstate war. The twenty years after the Second World War was a Pax Americana. By virtue of the tremendous damage suffered in the war by all the other powers, the United States became a global hegemon. America kept the peace (on American terms, of course) because no other country had the military or economic capacity to challenge it. This is the “great” America that some seventy-five million American voters in the last Presidential election were born in, and that many of them have been convinced can be resurrected by shutting the rest of the world out—which would be a complete reversal of the policy mind-set that made the United States a dominant power back when those voters were children.

By the nineteen-seventies, the rest of the world had caught up, and students of international affairs began to predict that, in the absence of a credible global policeman, there would be a surge in the number of armed conflicts around the world. When this didn’t happen, various explanations were ventured. One was that the existence of nuclear weapons had changed the calculus that nations used to judge their chances in a war. Nuclear weapons now operated as a general deterrence to aggression.

“O.K., maybe I need to change my life, or maybe you could just tweak my medication.”

Other scholars proposed that the spread of democracy—including, in the nineteen-eighties, the Velvet Revolution in Eastern Europe and the dismembering of the Soviet Union—made the world a more peaceable place. Historically, democracies have not gone to war with other democracies. It was also argued that globalization, the interconnectedness of international trade, had rendered war less attractive. When goods are the end products of a worldwide chain of manufacture and distribution, a nation that goes to war risks cutting itself off from vital resources.

In “The Internationalists” (Simon & Schuster), two professors at Yale Law School, Oona A. Hathaway and Scott J. Shapiro, present another explanation for the decline in interstate wars since 1945. They think that nations rarely go to war anymore because war is illegal, and has been since 1928. In their view, the signing of the Kellogg-Briand Pact was not a Dr. Seuss parable with funny characters in striped trousers and top hats. The treaty did what its framers intended it to do: it effectively ended the use of war as an instrument of national policy.

Then what about the Japanese invasion of Manchuria, the Italian invasion of Ethiopia, and so on, down to the Japanese bombing of Pearl Harbor? Those actions were carried out by nations that were among the Pact’s original signatories, and they clearly violated its terms. According to Hathaway and Shapiro, the invasions actually turned out to be proof of the Pact’s effectiveness, because the Second World War was fought to punish aggression. The Allied victory was the triumph of Kellogg-Briand.

O.K., so what about the deterrent effect of nuclear weapons? The spread of democracy? Free trade and globalization? Isn’t the Kellogg-Briand Pact just a case of post hoc ergo propter hoc—an exercise in feel-good diplomacy that happened to find confirmation many years later in a state of global affairs made possible by other means? On the contrary, Hathaway and Shapiro argue. If war had not been outlawed, none of those other things—deterrence, democracy, trade—would have been possible. The Kellogg-Briand Pact is the explanation that explains all other explanations.

Genuine originality is unusual in political history. “The Internationalists” is an original book. There is something sweet about the fact that it is also a book written by two law professors in which most of the heroes are law professors. Sweet but significant, because one of the points of “The Internationalists” is that ideas matter.

This is something that can be under-recognized in political histories, where the emphasis tends to be on material conditions and relations of power. Hathaway and Shapiro further believe that ideas are produced by human beings, something that can be under-recognized in intellectual histories, which often take the form of books talking to books. “The Internationalists” is a story about individuals who used ideas to change the world.

The cast is appropriately international. Many of the characters are barely known outside scholarly circles, and they are all sketched in as personalities, beginning with the seventeenth-century Dutch polymath Hugo Grotius, who is said to have been the most insufferable pedant of his day. They include the nineteenth-century Japanese philosopher and government official Nishi Amane; the brilliant academic rivals Hans Kelsen, an Austrian Jew, and Carl Schmitt, a book-burning Nazi; the American lawyer Salmon Levinson, who began the outlawry movement in the nineteen-twenties and then got written out of its history by men with bigger egos; and the Czech émigré Bohuslav Ečer and the Galician émigré Hersch Lauterpacht, who helped formulate the arguments that made possible the prosecution of Nazi leaders at Nuremberg and laid the groundwork for the United Nations.

The book covers an enormous stretch of historical ground, from 1603, when a Dutch trader attacked and looted a Portuguese ship in the waters outside Singapore, to the emergence of the Islamic State. The general argument is that it made sense to outlaw war in 1928 because war had previously been deemed a legitimate instrument of national policy.

The key figure in the early part of the story is Grotius, who, in contriving a legal justification for an obviously brigandly Dutch seizure of Portuguese goods off Singapore, eventually produced a volume, “On the Laws of War and Peace,” published in 1625, that Hathaway and Shapiro say became “the textbook on the laws of war.” Grotius argued that wars of aggression are legal as long as states provide justification for them, but that even when the justifications prove to be shams the winners have a right to keep whatever they have managed to seize. In Grotius’s system, to use Hathaway and Shapiro’s formulations, might makes right and possession is ten-tenths of the law.

That doesn’t sound like much of a legal order, but it placed some constraints on what nations could do. For one thing, it prohibited nations from going to war to recapture lost territory or other goods, since those were now in the lawful possession of the victor. For another, it required states that were not party to a war to remain neutral. This meant not just that nations couldn’t intervene militarily in someone else’s war; they could not change, for example, the terms on which they traded with the belligerents. They were, in effect, obliged to look the other way. Individuals were given a license to kill under the old system, but only if they were already at war. Otherwise, killing was still just killing.

Hathaway and Shapiro argue that Grotius’s law of war explains why actions that look like simple landgrabs, such as the Mexican-American War, which began in 1846, were perfectly legal undertakings. They explain that the United States had a valid justification for attacking Mexico—among other things, they say, there was a matter of unpaid debts—and that it also had a right to whatever territory it could lay claim to as a result, which, in that case, included all or part of what would become California, Utah, Nevada, Arizona, New Mexico, Colorado, and Wyoming. The Mexican-American War was not an extralegal military adventure. It was how nations behaved in what Hathaway and Shapiro call the Old World Order.

The Old World Order obviously set a low bar for going to war, which was convenient during a period of imperial expansion but dangerous when the imperial powers turned on one another. In 1914, Grotius’s chickens came home to roost. The First World War was a regional brush fire that turned into an out-of-control inferno almost overnight. The system was not working, and the outlawry movement was a response to the emergency.

The outlawers reasoned that, since the old system had rested on the legality of war, the way to replace it was to make war illegal. Hathaway and Shapiro tell us that Salmon Levinson used the analogy of duelling. There had been many efforts to change the codes of duelling and make it more humane, but people still duelled. Finally, duelling was banned, meaning that killing someone in a duel was murder, and duelling stopped. The way to stop war was, likewise, to remove its legal immunity.

Hathaway and Shapiro acknowledge that one reason the Kellogg-Briand Pact is regarded as historically insignificant is that it provided no enforcement mechanism. The language of the Pact reads as merely aspirational, not much more than a promise to be good. The ineffectuality of the League of Nations, created in the wake of the First World War, was part of the problem. When Japan invaded Manchuria and eastern Mongolia, in 1931, creating the puppet state of Manchukuo, the League, which the United States never joined, judged Japan’s actions to be illegitimate. Japan responded by resigning from the League. Members of the League were in a bind: they could condemn aggression, but, as signatories to the Paris Peace Pact, they were prevented from going to war to stop it. The world needed not only a New World Order but also a way to make it stick.

This was provided by Nuremberg. From a realist point of view, the Nuremberg trials, which were conducted in 1945 and 1946 and resulted in death sentences for twelve Nazis, were an application of victor’s justice. Kennan called the trials a “horror.” The man who would become the leading international-relations theorist in postwar American academia, Hans Morgenthau, himself a Jew who had fled Hitler, considered the trials “a symptom of the moral confusion of our times.” “German aggression and lawlessness were not morally obnoxious to France and Great Britain as long as they were directed against Russia,” he pointed out. But the defendants were charged in three categories: crimes against the peace, war crimes, and crimes against humanity.

Winston Churchill was against holding trials at all. He thought the leading Nazis should be shot on sight. Joseph Stalin favored the trials. His country had been invaded and nearly conquered, and he wanted a precedent that made wars of aggression a crime. By the time the trials began, in October, 1945, the world knew of the death camps, and to many people it seemed unconscionable not to hold the surviving Nazi leaders accountable.

The chief U.S. prosecutor, Robert Jackson, characterized German aggression in his celebrated opening statement as “a crime against international society which brings into international cognizance crimes in its aid and preparation which otherwise might be only internal concerns. It was aggressive war, which the nations of the world had renounced.” In other words, Germany’s violation of the Kellogg-Briand Pact opened the door to the prosecution of crimes against humanity. (This also explains why Soviet atrocities committed during the war were not subject to prosecution. The Soviets had been engaged in a war of self-defense, and thus, in principle, had immunity for acts performed in its pursuance.)

But the legal basis for charging individual Nazis was flimsy. Technically, the Kellogg-Briand Pact had not made war a crime; it had simply removed the legal immunity that had been extended to it under Grotius’s system. And, according to international law, states, rather than individuals, were responsible for war crimes. In order to prosecute the defendants at Nuremberg, the Allies and their lawyers basically had to convert the Pact into a criminal code that made individuals liable for illegal acts of war. They did, and that is the most important legacy of Nuremberg today. It is what has allowed the prosecution, in an international court in The Hague, of more than a hundred and fifty individuals for war crimes committed during the fighting that took place in the former Yugoslavia in the nineteen-nineties.

Hathaway and Shapiro concede that, in its final judgment, the Nuremberg court reverted to a form of reasoning that Allied lawyers had warned against: it argued that, since the defendants should have known that their actions were wrong, the court was justified in punishing them—effectively an exercise in ex-post-facto legislation. But the trial marked the inauguration of a new international era, because it showed how the new order’s rules could be enforced.

It also signalled the advent of a new international understanding of the laws of war. From then on, territory seized by conquest in a war of aggression wasn’t exempt from reparations. Hathaway and Shapiro say that virtually all the conquered territory that had been unrecognized by the international community since 1928 was restored after 1948.

As Hathaway and Shapiro see it, the success in establishing this New World Order has brought “seven decades of unprecedented peace and prosperity.” That success has come at a price, however. When the United Nations was founded, in 1945, there were fifty-one member states, and the architects of the U.N. buildings left room for twenty more. Today, there are a hundred and ninety-three U.N. members. This is, in part, because the ban on conquest has allowed small states to maintain their sovereignty. But it has also produced a number of internally weak states, and a great deal of the carnage around the world today is the result of intrastate conflicts or the emergence of militant groups in states whose governments lack the power to suppress them. The Islamic State is an example of the kind of insurgency that thrives in weakened regimes. Atrocities seem endemic to such intrastate conflicts.

Hathaway and Shapiro are lawyers, and, in making their case for the supreme explanatory power of Kellogg-Briand, they litigate themselves around some tricky historical corners. The claim about the return of conquered territories turns out to require some definitional parsing. They mean what they call “unrecognized transfers,” a category that does not include, for example, Poland, Czechoslovakia, Romania, Hungary, Bulgaria, Albania, and East Germany, which became puppet states of the Soviet Union. Nor does their definition include the Baltic states, which were taken over by the Soviets in consequence of an agreement that Stalin made with Hitler. Hathaway and Shapiro argue that the United States refused to recognize this seizure, but this is not the reason those states were awarded independence in 1991. That happened because the Soviet Empire collapsed.

Hathaway and Shapiro acknowledge the Israeli annexation of East Jerusalem after the Six-Day War, in 1967, but say almost nothing about the West Bank. They scarcely mention America’s two Iraq wars, and they ignore the eight-year Iran-Iraq War that preceded them, which they presumably regard as a border dispute. (In the end, no territory changed hands, but almost half a million people were killed.) Part of the interest of their deeply interesting book, though, is seeing how far and in which cases you are willing to go along with them.

“The Internationalists” has some lessons for today. One is a warning against the temptation nations have to construe threats of war as equivalent to acts of war. The New World Order would seem to rule preëmptive strikes out of bounds, but not self-defense, and it’s easy to see how the latter might be made a justification for the former. The claim that Iraq had weapons of mass destruction was such a case, and the current standoff with North Korea might become another one.

Hathaway and Shapiro also argue that, to the extent that there is peace among nations, it is secured by the networks of international organizations and treaties that have proliferated since the Second World War. The authors count two hundred thousand international agreements now in force. These allow for a method of punishing international lawbreakers and outlaw regimes by what they call “outcasting.” Since there is no rule requiring neutrality, countries can now band together to impose sanctions on aggressors, casting truant nations out of the international system. This is how the world is responding, for example, to the forced annexation of Crimea. (It is not, on the other hand, how it responded to Iraq’s seizure of Kuwait, in 1990. Within six months, an international coalition of thirty-two nations, led by the United States, had attacked Iraqi forces and driven them out. The punishment chosen for violations of the new law of war depends a little on the size of the truant.)

Today, we are living through a backlash against globalization, and Hathaway and Shapiro see this as itself a serious danger to peace. “Trade plays an essential role not only as a source of beneficial collaboration,” they say, “but also as a collective tool for constraining illegal behavior.” Economic interdependency creates a harmony of interests.

“The Internationalists” doesn’t use the terms “realism” and “idealism,” but if it did, its point would be that policies once disparaged as idealistic turned out to have significant tangible consequences. Still, great powers do not give up something for nothing. A central phenomenon in modern world history is Western imperialism and its aftermath, decolonization. Western world conquest began in the fifteenth century and peaked in 1939, when seven European nations had jurisdiction over almost a third of the world’s population. After 1945, those empires began breaking up; by 1970, apart from a few, mostly short-lived holdouts, they had vanished.

These historical developments underlie many of the changes in the legal status of military conflict that Hathaway and Shapiro bring to our attention. So, for example, when they assert that “the likelihood that a state will suffer a conquest has fallen from once in a lifetime to once or twice in a millennium,” and support the claim with data comparing the amount of territory conquered annually between 1816 and 1928 with the amount conquered annually after 1948—it was many times greater in the earlier period—they are only recording the difference between a period of intensive empire-building and a period of imperial divestment.

“It is likely no coincidence that Grotius’s new theory favored sovereigns and their trading companies,” Hathaway and Shapiro note. Well, yes. International law is the superstructure for the system of geopolitical relations. In writing his law of war, Grotius claimed to be deducing from the principles of natural law the proper rights of states. But he was clearly inducing from the actual actions and ambitions of powers like the Netherlands a set of rules that legalized their behavior. Ideas like Grotius’s mattered because they provided a coherent rationale for what was happening in the world willy-nilly. Grotius made the world safe for imperialists.

Similarly, today, as Hathaway and Shapiro acknowledge, “the New World Order is not divorced from global power dynamics.” The Allied powers that went to war against Germany and Japan in the name of self-determination—which is the main principle of the Atlantic Charter, signed by Roosevelt and Churchill in 1941—all had imperial possessions. After the Second World War, the European powers could no longer afford those empires; in places where they tried to hold on to them—Algeria, Vietnam, Kenya—they paid a heavy price (to say nothing of the toll paid by the colonized peoples) and lost them anyway. Decolonization, assuming that the ex-imperial powers could maintain favorable trade relations, eliminated administrative costs and the associated ideological contradictions.

It is not surprising that the great powers, in a world in which their influence and their share of global product were likely to shrink, were willing to exchange the right of conquest for globalization, with its system of international trade agreements. “The Pact appealed to the West because it promised to secure and protect previous conquests, thus securing Western Nations’ place at the head of the international legal order indefinitely,” as Hathaway and Shapiro rightly say. Like most international treaties, it didn’t redistribute political capital; it locked in existing power differentials. Defining “conquest” as a violation of international law today means that it is much harder for smaller states to become big ones, and making smaller countries dependent on their trade with bigger ones keeps them in line. That there will be better off and worse off is always implicit in the concept of order. ♦

This article appears in other versions of the September 18, 2017, issue, with the headline “Drop Your Weapons.”

  • Louis Menand has contributed to The New Yorker since 1991, and has been a staff writer since 2001.

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