“You have no idea how much it contributes to the general politeness and pleasantness of diplomacy when you have a little quiet armed force in the background,” the diplomat-historian George F. Kennan declared in 1946. With his customary wit, Kennan enunciated a profound general principle: War and diplomacy are inextricably linked, and it is as great a mistake to conduct diplomacy without considering military means as it is to wage war without diplomacy.

This truth has never enjoyed universal acceptance, but in modern times the conviction—or wish—that diplomacy can prevail without any connection to the use of force has become much more widespread. Many see war simply as the failure of diplomacy rather than its complement, and some argue that statesmen should not even consider using military power until they have exhausted all other means of achieving their aims. It is not only the evil of war that animates these critics, but the belief that force makes any kind of diplomacy all but impossible—that the angry “blowback” of elite and popular opinion in other nations necessarily overwhelms all diplomatic efforts, traditional or public, and outweighs any advantages that force may bring. “Hard” power and “soft” power, in other words, are mutually exclusive.

Reality is more complex. As Kennan suggested nearly 60 years ago, when states act militarily without clearly defined political objectives supported by skillful diplomacy, they risk undermining their military successes by creating significant long-term problems. So, too, states that attempt to conduct complicated and dangerous diplomatic initiatives without the support of credible military options frequently fail to accomplish even their immediate goals—and sometimes create more severe long-term problems. The greatest danger lies neither in using force nor in avoiding it, but rather in failing to understand the intricate relationship between power and persuasion. Some rulers rely excessively upon the naked use of force, some upon unsupported diplomacy. History shows that the most successful of them skillfully integrate the two.

One of the keys to success in this endeavor lies in defining national ends that leaders and publics in other countries find at least minimally palatable. One can be an able diplomat and a talented commander on the battlefield, but even both abilities together will not bring success if they serve objectives that the rest of the world cannot tolerate. For the United States, there is no path that will spare it criticism and even outright opposition, but its broad goals of spreading freedom and political reform are ones that a great many people in the Muslim world and beyond will be able to accept. The challenge is not only to continue balancing power and persuasion but also simply to continue—to persist in the face of adversity and despite arguments that the very exercise of power ensures that the United States will never persuade and never prevail.

Napoleon Bonaparte offers the classic example of the perils of failing to set goals that other states can accept. Napoleon was a skillful diplomat, and he shrewdly used the seemingly invincible army he commanded to threaten the destruction of any European state that tried to resist him. In 1809, he persuaded Tsar Alexander I to send a Russian corps to his aid against Austria, but then, in 1812, the Aus­trians, along with the Prussians, marched alongside him when he invaded Russian soil. He was also  one of the most aggressive prop­a­gan­dists of all time, so successful that his propaganda continues to influence our perceptions of his era two centuries later. The “bulletins” he published regularly advertising his military successes were so effective that even today the myth that “thousands” of Russian soldiers drowned in waist-high water at the Battle of Austerlitz in 1805 lives on, despite numerous cogent refutations of it. His somewhat cynical use of French revolutionary propaganda to support his counterrevolutionary agenda made his propaganda more palatable both to contemporaries and to modern historians.

Yet Napoleon failed spectacularly to establish a stable and long-lived European peace based on French hegemony. He could never define a goal for himself that the rest of Europe found acceptable. When war broke out in 1803, he initially focused on defeating his archenemy, Great Britain. However, he so alarmed the other states of Europe with his aggressive assaults on British interests around the continent that, in 1805, they formed a coalition to fight him—the first of four coalitions that would be formed to stop him over the next decade. His victory over the first coalition at Austerlitz increased his appetite, and, by 1806, he had incited neutral Prussia to attack him. Victory in that conflict brought Napoleon’s armies to the Russian border and established an apparently stable peace.

But the French emperor continued to revise his aims, seeking more control over European affairs with each new military success. By 1809 he had so antagonized the Austrians, whom he had crushed in 1805, that they launched a single-handed war against him. His victory in that conflict led Tsar Alexander to abandon the notion that he could live with Napoleon and to begin military preparations that would lead to war in 1812.

By the time Napoleon and his troops began their disastrous retreat from Moscow in the winter of 1812, however, all the other powers of Europe had decided that his goal was nothing less than universal conquest and that they faced no challenge more important than defeating him. Emboldened by the destruction of the myth of Napoleon’s military invincibility, the major powers of Europe banded together into strong coalitions that finally defeated him on the battlefield and, in 1815, exiled him to St. Helena.

Diplomacy is not simply the art of persuading others to accept a set of demands. It is the art of discerning objectives the world will accept—and the restraints on one’s own power that one must accept in turn. Peace can endure after conflict only if all the major players find it preferable to another war.

Otto von Bismarck understood this principle better than any other statesman of modern times. He directed Prussia’s diplomacy through the Wars of German Unification (1864–71), which created the German Empire and brought all the German-speaking lands except Austria under Berlin’s control. None of the other great powers was initially in favor of Prussian expansion, and both Austria-Hungary and France were determined to fight rather than permit it. Like Napoleon, Bismarck did not rely simply on military power. He succeeded through a combination of public and private diplomacy almost unequaled in history.

Bismarck used official diplomatic procedures and back-channel communications with enemies and potential enemies, but he also used the news media to shape public opinion. He succeeded, for example, in making the Franco-Prussian War of 1870–71, a war of outright Prussian expansionism, appear to be the fault of the French. At a time when the two powers were engaged in testy negotiations over the future of Spain, Bismarck released to the press the “Ems Telegram.” He had carefully edited this dispatch from a Prussian official to suggest that the French ambassador had suffered a great insult at the hands of the Prussian king. Bismarck, who famously remarked that the doctored telegram would have the effect of a red rag on the Gallic Bull, got just the results he had hoped for. An indignant French public clamored for war, and in July 1870 the French government granted its wish. Austria-Hungary, which might have joined the French, was deterred by Bis­marck’s success in putting the onus of war on the French, along with his deft reminders about the catastrophic defeat Austria had suffered at the hands of the Prussians in 1866. The Prus­sians quickly destroyed the French armies of Napo­leon III, and the new empire of Germany emerged as the most powerful state in continental Europe.

Bismarck’s military and diplomatic derring-do could well have led to the other European powers banding together in coalitions against Germany, years of unremitting warfare, and the collapse of Bismarck’s policy. None of that ensued after 1871, for three main reasons: the military success of the Prussian army, Bismarck’s ability to define a goal that the rest of Europe could live with, and his willingness to use the power Germany had acquired to reinforce a stability desired by the rest of the continent. However much Prussia’s foes resented the new order, they feared fighting Prussia again even more.

Bismarck was wiser than Napoleon. Instead of allowing his appetite to grow with the eating, he determined to moderate Prussia’s goals and he worked to persuade the other European powers that Germany had no further designs on their territory. He also wielded Germany’s recently won power flexibly to preserve a new European stability, opposing adventurism by Russia and Austria-Hungary and using the threat of intervention by the German army to insist upon peaceful resolution of international disputes.

Bismarck’s method of maintaining peace and stability in Europe was so successful that it endured until his re­moval in 1890, and the peace that it created lasted for another 24 years. War supported diplomacy; diplomacy supported war. Each served clearly defined goals that even the defeated states could live with. That policy was the key to Bismarck’s success—and its absence the key to Napoleon’s failure.

Some will argue that the United States today is in a more complex situation than that faced by 18th- and 19th-century leaders. The terrorist threat is more akin to an insurgency in the Muslim world than it is to traditional power politics. Insurgency is, indeed, a special case of warfare. Unlike a conventional military struggle, which the great theorist of strategy Karl von Clausewitz aptly characterized as a duel, insurgency is a struggle between two or more groups for the support of the large mass of an undecided population. In such struggles, the counterinsurgent generally suffers more by resorting to force than the insurgent does. The role of any government, after all, is to ensure civil order and peace, and to protect the lives and well-being of its citizens. When the government takes up weapons against rebels, it places all of that in jeopardy, and the population is usually quick to resent it.

Still, there have been successful counterinsurgencies, even when governments used dramatically more force than the United States is ever likely to contemplate exercising in the Muslim world. One example is the Boer War (1899–1902), in which the British army suppressed an insurgency by Dutch settlers in South Africa only after burning farms and penning the bulk of the population, including many women and children, in barbed wire–encircled concentration camps. The hostility created by this conflict, the last in a series of Anglo-Boer wars over the course of decades, was enormous. As one historian of the period notes, “Far from destroying Afrikaner nationalism, Chamberlain and Milner, Roberts and Kitchener, were the greatest recruiting agents it ever had.”

If modern critics of the use of force are correct, Britain’s actions should have fueled endless Anglo-Boer hostility and a permanent insurgency. Instead, they led to the rapid restoration of relations with South Africa, which served as Britain’s loyal ally during World War I, sending thousands of soldiers to fight alongside their former enemies. Why did this transformation occur? Britain’s military victory was critical. The harsh tactics the British used broke the back of the rebellion and served as an effective deterrent against future Boer attempts to fight them. At the same time, the British government offered moderate terms of surrender—so moderate that some critics in Britain said it “lost the peace.” The Treaty of Vereeniging of 1902, modified substantially in 1907, left the Boers very much in charge in South Africa, although under overall British suzerainty.

A perhaps even more apt example comes from the end of World War II. In Germany and Japan, the American occupiers were far from welcomed, and it is not hard to understand why. Even some official U.S. military histories acknowledge the triumphant GIs’ extensive looting and mistreatment of the local populations in Germany. But the sheer scale of the U.S. military victories in Germany and Japan helped prevent the development of significant insurrections or opposition movements. Neither the Ger­mans nor the Japan­ese were willing to risk further destruction of their society.

The nature of the peace settlement, how-ever, promoted increasingly close relations between victor and van­quished. As the Marshall Plan was implemented in Ger­many and U.S. reconstruction efforts bore fruit in Japan, and as the United States and its allies worked to rebuild the German and Japan­ese polities along stable dem­ocratic lines, hostility toward America evaporated much more rap­idly than anyone had a right to expect. Of course, the growth of the Soviet threat played a crucial role, since it made the Amer­ican oc­cupation, even at its worst, seem more attractive than the Soviet alternative. And as the nature of the U.S. military presence shifted to protection against an ex­ter­nal threat, and Amer­ican economic and political aid continued to flow, the occupation came to be seen as a good thing by the majority of the German and Japanese populations.

Today, those who are most reluctant to consider the use of force under any condition except in response to direct attack pin most of their hopes on the United Nations and other international organizations. In these forums, they believe, states should be able to peacefully resolve even their deepest differences. But history shows rather conclusively that the same principles that govern the affairs of nations also govern those of international organizations.

In 1923, for example, Benito Mussolini seized the Greek island of Corfu and demanded an exorbitant “reparation” from Athens after several Italian officials were assassinated in Greece. No evidence then or since has proven that Greeks were involved in the killings, and it is at least as likely that Mussolini’s own agents were the culprits. The Greeks turned to the newly formed League of Nations.

Britain initially supported the Greeks’ request, but it was virtually alone among the major powers. Prime Minister Stanley Bald­win’s government had to choose: Forcing the issue into the League’s pur­view would create a serious risk of war with Italy; giving in to Mus­so­lini would destroy the League as an effective force in the post–Great War world order.

Baldwin found the task too daunting. Britain was war weary, and its forces were overextended and weakened by budget cuts (although it is clear in retrospect that the Italian navy could not have resisted the Royal Navy). In the end, the Greeks paid an indemnity they should not have owed, Mussolini abandoned an island he should never have occupied, and the case was taken away from the League of Nations. The precedent was thereby established for the Japanese invasion of Manchuria in 1931, to which the League made no response, and for the Italian invasion of Abyssinia in 1935, to which the League also had no meaningful reaction. The emasculation of the League in 1923 destroyed its credibility and virtually ensured its irrelevance in the major crises that lay ahead.

By contrast, the first Bush administration reacted to the Iraqi invasion of Kuwait in August 1990 in a manner designed not merely to resist Saddam Hussein’s aggression but to strengthen the United Nations and prepare it for a central role in keeping the peace in the “new world order” after the Cold War. President George H. W. Bush quickly decided that he would use military force to reverse the Iraqi action. This was the critical decision. Although the task looked difficult at the time—Iraq had the fourth-largest military in the world, and early American casualty projections were as high as 50,000—the president believed that he had to act to prevent the immediate unraveling of the international order and to forestall legitimation of the principle that powerful states could use force to prevail in territorial disputes with their weaker neighbors.

Bush began a massive diplomatic effort to gain allies for the United States, win over world public opinion, and, above all, acquire clear and strong sanction from the UN for the operation to liberate Kuwait. The UN was galvanized by Bush’s efforts. The discovery after the war that Saddam Hussein had been maintaining a vast weapons of mass destruction (WMD) program that had been virtually unknown to the principal international monitoring agencies led to a complete overhaul of those agencies, particularly the International Atomic Energy Agency (IAEA). Under its new director, Hans Blix, the IAEA and UNSCOM, the UN agency set up to oversee the destruction of Iraq’s WMD program, pursued an increasingly successful effort in Iraq, supported periodically by the threat and use of U.S. airpower.

By the late 1990s, however, a growing American reluctance to use that power allowed the Iraqi dictator to eject UN inspectors. Saddam then began mothballing his WMD programs but was able to persuade the world that he still had them. The inspections effort in Iraq had been effective only when supported by the threat and occasional use of American military force.

The IAEA enjoyed no such support in North Korea. By 1994, Hans Blix had discovered a number of violations of the terms of the Nuclear Non-Proliferation Treaty, and the North Koreans had begun to interfere with the work of the inspectors in critical ways. At first, the Clinton administration supported the IAEA in its struggle to force then-leader Kim Il Sung to come clean. As the crisis developed, however, the administration’s concern over the danger from the North Korean army overwhelmed its desire to support the IAEA’s efforts. The Clinton administration then brokered a deal with Kim Il Sung’s son and successor, Kim Jong Il, that allowed North Korea to keep skirting the inspections program. As a result, the IAEA was unable to prevent the North Koreans from developing a nuclear weapon—and all indications are that they now possess one or two nuclear devices. Not surprisingly, recent negotiations, similarly unsupported by military force, have also failed to curb the North Korean nuclear program.

It may be that, in the end, as with Adolf Hitler and a few other die-hard aggressive leaders, there is no finding a peaceful solution with Kim Jong Il. Or it may be that some unforeseen change within North Korea will yield such an outcome. It is certain, however, that diplomatic approaches unsupported by military power will not make much of an impression on Pyongyang, and that the continued failure to support international agencies charged with enforcing nonproliferation agreements will doom the cause of nonproliferation itself.

International organizations, especially those devoted to nonproliferation and peacekeeping, can succeed in difficult circumstances only when their efforts are supported by credible military means. Because such organizations help to identify current and future threats, and to galvanize international support behind the punishment of transgressors, the use of American power to support them is a good investment in long-term security.

George Kennan was right: The existence of a powerful and battle-proven military makes the job of diplomats and political leaders vastly easier. However unhappy a defeated people may be with a given political settlement, or however resentful of military actions carried out against them, very few will take up arms again if convinced that they will  again be defeated. Military half-measures designed to “send a message,” such as those the Kennedy and Johnson administrations used in the early days of the Vietnam struggle, deceive no one and leave the door open for insurgent victory. Clear-cut military triumph, such as the British achieved against the Boers, makes even the staunchest rebels more reluctant to try the test of battle again. The use of military force with any aim in mind other than victory is extremely dangerous and likely to be counterproductive.

Though the use of force may stir anger and resentment in an enemy population and damage a state’s position in the world community, history suggests that both the animosity and the damage may be more fleeting than many suppose, and that their scale and duration may depend on many elements other than the mere fact that force was used. By far the most important element is the acceptability of the peace conditions imposed by the victor after the struggle. If the victor can devise terms that most of its foes and the rest of the international community can accept, then the animosity is likely to fade quickly. And if acceptable terms are coupled with continued military power, then the prospects for a lasting and stable peace are excellent.

The actions of the victorious state in the aftermath of the war are of great moment in determining the long-term consequences of military action. If the victor remains engaged with the defeated power in a positive way, helping to reintegrate it into an acceptable international system, and even to make good some of the damage done by the military operations, then memories of the pain inflicted by the war can be surprisingly short. The rise of a new and dangerous common enemy—which is not as unusual as one might suppose—can dramatically hasten this process.

Diplomacy is not the opposite of war, and war is not the failure of diplomacy. Both are tools required in various proportions in almost any serious foreign-policy situation. Yes, it is vitally important for the United States to “work with” and “support” international organizations, but their success in the foreseeable future will depend at least as much on the strength of the American military and on America’s willingness to put its power behind those organizations. On that strength and on that willingness rests nothing less than the peace of the world.