When we wrote "The Internationalists," our aim was not only to offer a novel account of how the world order took shape—that a largely forgotten treaty signed in 1928 to outlaw war set in motion a process that transformed the way states behave. We also sought to counter the common view that law is irrelevant in a world of great power politics. This view is generally associated with the “realist” school of international relations. Yet it is held by many who would not necessarily identify themselves as realists, but instead as “neoconservatives” or even just skeptics of the power of law in the global arena.

The realist perspective is often treated as clear-eyed and tough-minded; its alternative, naïve and dangerous. But we show in "The Internationalists" that the opposite is true. The “realist” description of world affairs does not correspond with reality. It is at odds with major developments over recent generations that have delivered tremendous gains, from declines in interstate conflict to increases in global prosperity. Worse, this dismissive view is behind a truly dangerous trend: the increasing willingness of the United States and other nations to ignore or distort international law and institutions to use military force to resolve their disputes.

Our debate with the realists is woven into the fabric of "The Internationalists," but only occasionally surfaces. Here we address it directly, focusing on three commonly held beliefs—we call them “myths”—that our book aims to dislodge.

Myth #1: A change in the law cannot change how states behave.

The realist view tends to regard law as incapable of real influence. If a change in law is followed by a change in behavior, the argument goes, the change in law did not cause the change in behavior. These changes are merely epiphenomenal—powerful states caused both the law and the behavior to change at once. The decline in interstate wars, therefore, is chalked up to the decline in the desire of states for interstate wars. As one recent response to our book put it, “States still use violence and coercion when it suits them. It just so happens to suit them less these days.”

The Internationalists argues the opposite—law can bring real change.

In the book, we argue that the origins of the modern legal order can be traced to the decision of nearly every state in the world to sign a treaty in 1928 outlawing war. That treaty—the 1928 “Kellogg-Briand Pact” (sometimes also known as the “Paris Peace Pact” or “Pact of Paris”)—has been largely dismissed as a feckless attempt to end war through a misguided act of idealism.

It is impossible to appreciate why the common wisdom is wrong and how consequential the decision to outlaw war was without understanding how different the world once looked. The “Old World Order,” as we call the pre-1928 system, was defined first and foremost by the belief that war is a legitimate means of righting wrongs. Resorting to arms did not signal a failure in the international system: It was how the system worked. For states, war was an indispensable instrument of justice.

In the Old World Order, states had the legal right of war. This right, in turn, led to other legal rights. For example, states had the right of conquest. Since the function of war was to right wrongs, the point of conquest was to compensate the victim who had to wage war to recoup his damages. Likewise, soldiers and sovereigns could not be punished for homicide that took place on the battlefield because their behavior was legally protected. To kill someone outside of war was murderous; to kill millions in war was glorious. Similarly, neutral states were under a legal duty to stay out of the conflict. They were, therefore, prohibited from treating each side differently. The imposition of economic sanctions by a neutral state—the routine way in which states respond to aggression today—was illegal before 1928. Finally, states not only had the right to wage war to enforce their rights but also to threaten to wage war—thereby sanctioning the behavior that we now call “gunboat diplomacy.”

Remarkably, this entire set of rights began to unravel almost immediately after the Pact was ratified. How precisely the rules changed—and how those changes can be traced to the Pact—is a story that fills 200 pages in The Internationalists, so we will not repeat it here. But we will offer one example to illustrate the tectonic shift that the international system would undergo after 1928.

On September 18, 1931, Japan invaded Manchuria. The states that had just ratified the Pact faced a dilemma: how to enforce the prohibition on war. It would seem absurd to use war to enforce a prohibition on war. One solution was that the states of the world would refuse to recognize the conquest as legally valid. On January 8, 1932, U.S. Secretary of State Henry Stimson delivered simultaneous diplomatic notes to the governments of China and Japan stating: “[T]he American Government . . . does not intend to recognize any situation, treaty or agreement which may be brought about by means contrary to the covenants and obligations of the Pact of Paris of August 27, 1928.” According to the “Stimson Doctrine,” as the official U.S. policy became to be known, conquest was no longer legal or legitimate.

As we described in the book, and summarized in the New York Times, that change in the law closely tracks a remarkable change in state behavior—conquest, once common, became rare. States could expect to experience foreign conquest of some sort once in a human lifetime before 1928; now the data show that the average state will be subject to conquest at most once in a millennium. In virtually all cases since 1928, territory acquired by force has reverted to the nation that originally held it. And what boundaries determine who held that territory? The borders that existed when the Paris Peace Pact was ratified in 1928. The best explanation for this otherwise mysterious change in behavior is that non-defensive war had then become illegal and states lost their right of conquest.

To attribute the change in state behavior to the change in law is not to argue that states are necessarily acting out of a sense of legal obligation. Of course, some might: Law-abiding states might stop engaging in conquest because conquest is illegal. But others might not do so because, given the change in the law, conquest no longer pays. If the conquering state cannot get other states to recognize the spoils of war, what would be the point of conquest? Law often works in this indirect fashion, by affecting the incentives for states to act one way rather than another.

Not only did the rules change in ways that changed states’ incentives, but they did so rather suddenly. The Old World Order—legally-sanctioned conquest and gunboat diplomacy, immunity to prosecution for aggression and illegality of economic sanctions—gave way to a New World Order—the non-recognition of conquest and gunboat diplomacy, the crime of aggression and the legality of economic sanctions—in the few short years between 1928 and 1945. The rapidity of this transformation is very hard to explain from a realist perspective, but makes perfect sense on one which accords law causal efficacy.

This change in the rules, moreover, was not simply a result of the new United Nations Charter. The Charter did not come from thin air. The core commitment of the Allies to prohibiting war—which was embedded at the beginning of the Charter in Article 2(4)—were directly lifted from the Pact. Indeed, drawing on new archival research, we show that the very same person who ghost-wrote the Peace Pact also wrote the first draft of the UN Charter. He even copied the Pact’s language at the start of his first draft, making clear that he believed the Charter consolidated a transformation that began with the Pact in 1928, when the world legally renounced war as an instrument of justice.

Hence, the claim is not simply that we should shift the date on which the modern legal order began back 17 years—from 1945 to 1928. Our point is that the modern legal order is grounded in the decision to outlaw war. And that, in turn, changed the world order in deep ways not generally appreciated but profoundly important to the interests and behavior of states.

Myth #2: Power matters, and if power matters, law doesn’t.

Realists would credit the changes we describe above to shifts in power politics, such as the invention of nuclear weapons, or, as Max Boot claimed in a review of our book, to U.S. military alliances, such as NATO.

These claims are inadequate for a number of reasons. First, the changes that we describe in our book predate the invention of nuclear weapons or the formation of NATO. The key rules of the modern legal order began to change in 1932 and were fully in place by 1945.

Second, the view that power is all that matters fails to explain why nuclear weapons or military alliances have been used for defensive purposes. Why, when these nuclear states or military alliances are so powerful, have they not been used for non-defensive purposes? The United States briefly had unilateral control over nuclear weapons; why did it not use that opportunity to conquer the world? Of course, this seems an absurd suggestion—and that is precisely the point. The use of force for such purposes strikes us today as beyond the pale, but it was not always so. States regularly waged war for non-defensive purposes. The United States went to war with Mexico in 1846 to collect unpaid debts. Much of the West and Southwest of the United States is the United States—and not Mexico—because the United States conquered that land in satisfaction of monetary obligations. Why did the United States not use its hegemonic power to grow yet again? The answer, as we explain in the book, is that the United States and its allies have been committed since 1928 to a world in which aggressive war is outlawed; and they created institutions to enforce that commitment. Put simply, the decision to outlaw war is a basic assumption that all other explanations of the decline of war rely on but never make explicit.

To be clear: We recognize that power matters—a lot. What we reject is the claim that power is all that matters, and if power matters, law must not. We reject this account not because states or those within them care more about law than power. Instead, the choice between law and power is a false one. Real power—power useful for achieving important political objectives—does not exist in the absence of law. Law creates real power. States can reach their goals only if others recognize the results of their actions. As the Japanese found out in 1931, it was not enough to occupy Manchuria if no one treated Manchuria as Manchukuo. Russia is relearning this lesson today in Crimea. It can claim Crimea, but if the rest of the world does not recognize the claim, tourists from everywhere but Russia will vacation elsewhere, ATM’s will run dry, and the economy will wither away. China is discovering the same lesson in the South China Sea. It can occupy islands but they are worth little as long as the rest of the world refuses to recognize them.

Realists generally regard military power as the United States’ greatest source of influence. And there’s no doubt that the U.S. military is essential to its influence in the world. But relying solely on this power—and ignoring the power that comes from cooperating with like-minded states to create and enforce legal rules—will erode the country’s capacity for influence. President Trump’s attacks on NAFTA, the World Trade Organization, and the United Nations don’t make us stronger. They make us weaker by depleting our capacity to influence other states’ behavior without using force.

The Internationalists argues that militaristic adventurism in violation of international law poses a serious threat to the modern international legal order. Indeed, if our book could send just one message, it would be that using force to resolve disputes as many (though not all) realists and neoconservative thinkers have repeatedly urged, threatens to return us to a far darker world.

Myth #3: Relations between states are governed by geopolitical forces; individuals and ideas can’t make a real difference.

Realism is largely fatalistic. It leaves little room for human agency to improve the world. But the story of the transformation of the Old World Order into the New World Order demonstrates that even as law shapes power, ideas—and those who develop and spread them—shape the law. Brute force, like rushing water, must be controlled and channeled. Dams need to be built, canals dug, and pipes laid. Those who shape the laws are the hydraulic engineers of the political world. To be effective, they channel power.

The Internationalists for whom the book is named were transformative figures. They were transformative because of their ideas—and because they were willing and able to use their ideas to change the world. None were household names. None held high political office. None found his task easy. None, moreover, was able to accomplish much on his own. But each had a conviction about the way the world should be organized. And each was willing to fight for years, even decades, against long odds to take small steps along the path to constructing a new global order grounded in the rejection of war. The Internationalists worked with one another and with a vast array of grassroots groups, politicians, academics, government bureaucrats, and international colleagues to make progress.

Their example teaches us that we have an opportunity and a burden. Each of us, even those far outside the halls of government, has the capacity to make a difference. We all bear responsibility for the world in which we live. Together we can and must continue to support institutions that have kept the peace, adapt them to changing circumstances, and develop new ones that will further reduce violence.

Note: This post is adapted from the authors’ new book, The Internationalists: How a Radical Plan to Outlaw War Remade the World.