Louisa Thomas is the author of “Conscience: Two Soldiers, Two Pacifists, One Family — A Test of Will and Faith in World War I.”

DURING World War I, a conscientious objector named Evan Thomas faced a court-martial for refusing an order to eat during a hunger strike. The prosecutor’s real attack, though, was on Thomas’s refusal to serve in the Army.

“The very foundation of every civilized government from the first beginning of history down to the present time has been based absolutely upon force of arms,” the prosecutor argued. “Gentlemen, if we don’t punish these cowards who appear in this land like the sore spots on our bodies to the fullest limit of the law, this government cannot survive.” Then he asked for Thomas to be given the death penalty.

Such a scene would seem preposterous today, and not only because it is hard to imagine such a prosecutor. It is also hard now to picture a man like Thomas, who was my great-great-uncle: an Ohio-born Princeton graduate, a son of a middle-class minister — and a strict pacifist.

Pacifism is a curiosity. Even those few who call themselves pacifists are usually quick to qualify the word; they’re “realistic” or “pragmatic” pacifists. Rarely does anyone question the tragic view of human nature: man is aggressive, violence is a fact and some wars are necessary. It is tempting to say this is knowledge learned of experience. Fascism, communism, nuclear bombs, genocide and terrorism seem to confirm the futility of strict nonviolence. As President Obama said while accepting the Nobel Peace Prize, recognition of the moral and practical necessity of force “is a recognition of history, the imperfections of man and the limits of reason.”

A recognition of history, however, also compels us to remember that many Americans — as disparate as Andrew Carnegie and the Rev. Dr. Martin Luther King Jr. — have held another view. These pacifists (an imperfect, but useful, term) rejected organized violence on principle. They had different and contradictory motives and tactics, but their repudiation of war challenged the idea that man’s imperfections, and reason’s limits, made war acceptable. They were often naïve — but so were leaders who pursued policies that made armed conflict more likely, or who assumed that violence could be governed by good intentions and expertise.

Few people today openly espouse pacifist beliefs, even as the impact of 20th-century pacifism — from the United Nations to the Civil Rights Act — is everywhere apparent. In part that’s because some of the movement’s goals have come to pass: war is now usually less lethal and involves only professional soldiers, who take pains to minimize civilian casualties. Meanwhile, pacifists’ emphasis on the moral issues surrounding violence could be turned against them, especially during humanitarian crises or acts of foreign belligerence. War, in other words, has become harder to object to. But that doesn’t mean it’s not objectionable, or that pacifists don’t have a point.

BOTH pacific and martial currents run through American culture, and pacifism has struggled as much with its own principles as it has with the nation’s abiding militaristic streak. Seventeenth-century Anabaptists believed that nonresistance was purifying in a corrupted world. Colonial Quakers thought their refusal to fight would serve as a witness to God’s kingdom of peace and the sacred quality of individual life.

Early pacifists — long before they called themselves “pacifists,” a 20th-century word — were sectarian, but the winners of the Revolution also dreamed of lasting peace. Most were suspicious of standing armies and concentrated power, and they respected not only equality before the law but also the unruly demands of the individual conscience.

In the 19th century, faith in the rational, moral improvement of mankind, along with a revival of religious enthusiasm, spurred the peace movement. After the unpopular War of 1812, nonsectarian peace movements sprang up across the North, mostly appealing to well-educated white Protestants.

As the threat of war with the South grew, though, peace advocates struggled to define the limits of their stand. Were defensive wars permissible? Was peace that allowed terrible injustice worth keeping? And here the movement splintered. “O, yes — war is better than slavery,” wrote Angelina Grimké Weld, a political activist and strident peace advocate. The movement could not easily overcome the conflict between justice and peace — not then, and not a century later. Slavery had been abolished, but some 620,000 men in uniform had died.

The end of the war and the years of peace that followed, however, allowed many to put off the question. Late-19th-century Americans placed their faith in the progress of history. After the carnage of the Civil War and, in Europe, the Napoleonic wars, many believed that humanity had learned its lesson, and that world peace was a real possibility. Peace societies flourished. Activists formed international networks. A Swiss businessman established the Red Cross in 1863. At peace conferences at The Hague in 1899 and 1907, delegations established rules for neutrals and treatment of prisoners of war, and even an international arbitration court, in the hope of restraining warfare. (The most urgent reforms, like arms limitations and enforcement mechanisms — anything that might really limit state power — were off the table, but the conferences seemed a start.)

Money fueled the hope. In 1896 the inventor of dynamite died and left a will establishing the Nobel prizes, including one for peace. In 1910 Carnegie gave $10 million to found the Carnegie Endowment for International Peace. “Business pacifism” became a first principle of the Gilded Age. “Dead men buy no clothes,” said one industrialist in 1907.

But the difficulties of reconciling pacifist ideals with the reality of global politics remained. When world war came, most of the peace advocates in Europe and, eventually, the United States joined the fight, not because they were rejecting their own beliefs but because they were told repeatedly that it would be a war to end war. Only a tiny minority, including Evan Thomas (whose lifetime prison sentence was reduced to 25 years before he was released on a technicality), refused to fight.

Many would come to regret their support. Some retreated into isolationism. But others redoubled their efforts. International peace movements revived. Governments tried outlawing war (the 1928 Kellogg-Briand Pact is still on the books). Students held antiwar protests and signed pledges to refuse to fight. Peace advocates and statesmen wrestled to build the League of Nations. Time magazine chose Mohandas K. Gandhi man of the year in 1931. For a brief moment, pacifism seemed to be a driving force in international politics.

It wasn’t to last. And while some peace activists quickly recognized the danger of fascism, others wanted to wish the threat away. Isolationists and pacifists formed awkward alliances, until even the most ardent of them admitted that war had become unavoidable. In the United States, for the most part only absolute pacifists resisted the war after Pearl Harbor. In the eyes of most Americans, including erstwhile pacifists, the war seemed to disprove for good the belief that all violence was bad. There was, it appeared, such a thing as not only a just war but a “good” war.

But the good war was also a total war. The Nazis were defeated and the concentration camps liberated, but mankind had also figured out how to destroy itself. Aerial bombing killed indiscriminately and atomic bombs incinerated two cities.

One result was a contradictory postwar world. On one hand, global peace seemed all the more pressing. Even President Franklin D. Roosevelt, who took the United States to war, recognized the need for permanent peace from the start: one of his 1941 Four Freedoms was that from fear, which meant, he said, “a worldwide reduction of armaments to such a point and in such a thorough fashion that no nation will be in a position to commit an act of physical aggression against any neighbor — anywhere in the world.”

The international community built on that dream, trying to redistribute power so that no nation would attack any other. Statesmen established the United Nations in 1945 and worked out strict international laws, greater democratic freedoms and social justice, and enforcement mechanisms for collective security.

Still, the hope was damaged. Visions of permanent conflict, not harmony, prevailed. The peace movement itself spent the early cold war years in the wilderness. The global spread of the bomb would help revive it, but in some important ways it became more strategic than pacifist in its principles. Nuclear deterrence and test bans drew some of the broadest support, appealing to mothers who worried about nuclear contamination in milk rather than nuclear weapons outright. The coalitions were fractured as different groups had their own aims and ambitions, some narrowly antiwar, others for broader social justice. They did not easily coexist. Pacifists were often a minority, and absolute pacifists fewer still.

Indeed, the 20th century not only shattered the hopes of turn-of-the-century pacifists, but its carnage seemed to disprove the possibility of abolishing war. American peace movements could not stop war in Korea, nor keep the nation out of Vietnam. That war, of course, would spur the largest network of antiwar movements in American history. But it succeeded in part by riding a countercultural tide — and, already weakened by internal tensions, it was subsequently hammered in the post-60s backlash. Chastened, many antiwar activists kept their attention on nuclear weapons.

Pacifists had their real success when they focused on organized violence at home — and nowhere more so than in the civil rights movement. Inspired by Tolstoy and Gandhi, pacifists like Dr. King, James Farmer and Bayard Rustin demonstrated the power of nonviolent protest in forcing social and political change, developing techniques still used today in groups as diverse as the National Organization for Women and the Tea Party.

Nonviolent movements continue abroad, most recently in parts of the Middle East. It is not just idealism that drives them to reject force; they also know it works. A study conducted by Erica Chenoweth of Wesleyan University and Maria J. Stephan of American University found that of hundreds of insurgencies from 1900 to 2006, more than 50 percent of nonviolent campaigns worked, while only about 25 percent of violent ones did.

FOR the most part, though, nonviolence and pacifism in the United States are today discredited as utopian, hippieish or narrowly religious, more anti-American than anti-war. There are still people who say that force only destroys, that its consequences are uncontrollable, that it is unethical — but those critiques trouble us on the margins, or in books or movies. There are still a few antiwar groups (not all of them pacifist) — the War Resisters League, the Fellowship of Reconciliation, the Albert Einstein Institution — but hardly any serious public figures take the stage to defend their views.

Some of what the American peace movement fought for has come to pass: there is no draft, there are no special taxes raised to pay for war, the threat of nuclear Armageddon has receded and the country plays a leading, if controversial, role in multilateral institutions. Rooting out terrorists and intervening in civil conflicts, soldiers often do more police work than conventional combat.

The results have been mixed, though, and in some ways at odds with pacifism’s longer-term goals. Most people don’t want to think of war, and thanks to the lack of a draft, most don’t have to. Huge worldwide protests against sending soldiers into Iraq in 2003 were a sideshow for many people. Significant antiwar sentiment over the Iraq and Afghanistan wars has mostly challenged the time, the place, the conduct and the costs of deployment, not the use of force itself. Those who are on active duty — less than one percent of the population — and their families bear most of the burdens.

Such complacency has allowed for the possibility of unending war. Because of the nature of intelligence gathering and weapons technology like drones, the government can use deadly force without popular support or approval. The president has claimed — and we have given him — extraordinary powers.

We should respect the sacrifices of soldiers and the complexity of governing in a dangerous world. But war has a way of coming home, eroding our democratic culture as well as our safety. American pacifists of the past knew that, and we need people like them today: people who don’t believe war is inevitable, who will challenge what we assume and accept, and who will work to end it.