In an unsettled time, with an unsettling president, many Americans are unsure of their conception of the world and their country's role in it. What should the United States be doing — if anything — to shape the global order? To answer this question, we need to better understand ourselves and our history.

Americans regularly make three curious and contestable claims about peace. First, they often assume that they are a peace-loving people, that our republic has been a force to promote amity in the world. Second, they assume that peace is an unalloyed good, both a tool and product of progress, providing incontrovertible benefits; war and conflict, meanwhile, have brought nothing but misery and disaster. Third, they see peace and order as the natural state of the world, and view any force that disturbs this harmony as both anomalous and deviant, to be identified, isolated and eliminated.

It is easy to understand why Americans embrace these views. If the U.S. and its citizens and values are associated with peace and stability, then actions that might typically be understood through the narrow lens of self-interest can instead be translated into selfless policies that benefit mankind. This belief is at the heart of American exceptionalism: the idea that the U.S. has a unique and revolutionary history and mission. Seeking no gain for ourselves, we are different from empires and other states. Founded in liberty, the U.S. by its very nature spreads the blessings of its own political system when it acts in the world. As philosophers such as Rousseau and Kant made clear, a key blessing of a system of liberty is friendship among men, and peace among nations. Peace must therefore be in very nature of who Americans are.

Or so the story goes. But an honest portrayal of our own history, and that of world politics over the past few centuries, casts doubt on all three assumptions.

Does the American nation have a history of working toward peace and stability? The U.S. was born in war. The American republic was also the product of the great power competition it later disdained. America was a fiercely contested battlefield during the Seven Years War, and the British victory left its powerful rival, France, eager for revenge. French aid and military support not only made independence for the American patriots possible. It also bankrupted France, ushering in decades of revolution and war in Europe.

The young republic returned this favor by rapidly expanding on its continent, frequently with force or the threat of force, and picking quarrels with other states. Often it was the American people themselves who demanded war. The U.S. government was able to suppress the popular desire to conquer Cuba and Canada, but failed to constrain the war spirit against Mexico in 1845 or Spain in 1898.

Even in times when the U.S. was supposedly isolationist, it flexed its military muscles. Whether Commodore Perry's gunboats sailing into Tokyo Bay or the long, bloody counterinsurgency in the Philippines, the U.S. never eschewed the threat of force in its relations with the world. The truth is, the history of Americans and their state is steeped in war and conflict.

Was this aggressive American behavior out of line with how most states behaved? Looked at through a broader lens, a passion for war was recognized as an essential part of any national mission and as a driver of progress. War and military competition in the 17th and 18th centuries, for example, transformed England from an isolated island monarchy into a dynamic world power. The rise to global strength came at great cost in blood and treasure, but brought other benefits as well — improved and more responsive governance were needed to deliver legitimacy to the state that taxed its citizens to pay for war, while sophisticated financing demanded improved consistency and accountability to foreign creditors. War also created new technologies, an emerging middle class and the seeds of an industrial revolution.

Every historian knows this uncomfortable fact: War and great power competition have generated both misery and extraordinary human progress in the modern era. As William McNeil explained in his classic, "The Pursuit of Power": "a profound ambivalence inheres in warfare and organized violence." The need to protect your people and advance your interests in a dangerous world drove extraordinary advances in technology, improvements in governance, and great increases in wealth and prosperity. Whether improved medical techniques to save the wounded or the mass education provided to produce literate armies, progress and war went hand in hand in the West.

Perhaps even more uncomfortably, the celebration of war and its memory shapes a nation's sense of itself, its patriotism, its cohesion. Imperial China's isolation and relative security during the same period as Great Britain's bloody rise may have prevented similar innovation and national unity, and left the once great power vulnerable to European powers tested by more than a century of intense military competition.

We know and hate the cost of war. Yet we must acknowledge our present age of technological marvels and political progress emerged from conflict. More important, war is sometimes needed to protect our people and our values. Dangerous states and evil leaders can exploit the admirable desire for peace. Even in more recent times, efforts to maintain peace at all costs can be viewed with disdain, as British Prime Minister Neville Chamberlain and his appeasement of Hitler at Munich are remembered with scorn.

This leads to the final assumption most Americans make: that peace and stability are and always have been the most desired goal of peoples and states. We are also told that the world has moved inexorably to a more peaceful, ordered condition, following the inalterable arc of history. By that same logic, peace should be easy to keep and requires little effort, save for isolating and defeating the unusual states or forces that seek to interrupt it.

This last belief is perhaps the most dangerous. The relative peace of the last eight decades has been the exception, not the rule. It has been hard won and could be easily lost. An accurate understanding of that period is therefore all the more important, especially since the U.S. was the key actor in making it happen.

The first half of the 20th century proved that the hellish suffering of unrestrained war far outstrips its benefits. War, revolution and instability killed, maimed and dislocated tens of millions between the start of the First World War and the end of the Second. As McNeil pointed out, "organized and deliberate destruction of life and property" became "profoundly repugnant to contemporary consciousness, especially in view of the quantum jump in capacity to kill impersonally and at a distance."

This would have been true without the invention of that most terrible of weapons, first atomic and then thermonuclear weapons, and the capacity to deliver them anywhere on the globe in a matter of minutes. The large-scale use has the potential to end civilization as we know it. Peace was not only a desired hope of world politics; it became a necessity.

How would such an outcome be achieved? Few living in 1945 would have thought the elimination of great-power war was possible, nor would they have believed that states would abstain from acquiring and using the most modern, fearsome weapons available. The U.S., however, committed to try. It did so by nurturing a world order, at great burden and risk, and in cooperation with other nations.

Most important was a U.S. commitment to engage and stay in the world — not episodically, but on a permanent, deep basis. This obligation took many forms: constructing and supporting robust international institutions, encouraging emerging democracies, international law, and human rights, and building and maintaining a stable and prosperous global economic system. It also required a harder edge. For the first time in its history, the U.S. mobilized and deployed abroad a large peacetime military and entered into political and security alliances with nations around the world. It committed to preventing the spread of nuclear weapons and reducing the likelihood of their use. And it demonstrated a willingness to use force, at great national cost and controversy, in conflicts where national interests were not immediately and obviously at stake.

This postwar American behavior was hardly inevitable. After all, the U.S. has possessed the world's largest economy for more than 125 years, and the U.S. share of world GNP in 1900 was not much different than it was in 1980 or today. Before 1950, the U.S. generally avoided international institutions, eschewed permanent alliances, demobilized during peacetime, had strong civilian control of the military, and allowed Congress an equal and sometimes greater voice in determining America's foreign relations. The need to guarantee peace in the nuclear age caused the U.S. to transform every one of these traditions.

History tells us that global peace is neither natural nor inevitable. Peace is the unusual, unnatural state, for the world and especially for Americans. This is what makes the post-1945 world so remarkable, and America's crucial role in building it so important.

At this crucial moment, when U.S. relations with the world are unfixed and uncertain, we forget this history at our peril.

Francis J. Gavin is the Giovanni Agnelli Distinguished Professor and Inaugural Director of the Henry A. Kissinger Center for Global Affairs at Johns Hopkins University's School of Advanced International Studies. He wrote this article for Bloomberg View.