Unshakeable resolve. The theme was a touchstone on the evening of September 11, 2001, as members of Congress gathered on the steps of the Capitol Building. The Republican Speaker of the House of Representatives, Dennis Hastert, announced that “Democrats and Republicans will stand shoulder to shoulder to fight this evil that’s been perpetrated on this nation.” The Democratic Senate Majority Leader, Tom Daschle, said that Congress: “will speak with one voice to condemn these attacks, to comfort the victims and their families, to commit our full support to the effort to bring those responsible to justice.” A day that began in fear that the Capitol Building itself would be destroyed, ended in a tableau of togetherness, as congressmen warmly embraced.

And then it started. A soft and calming sound at first: “Stand beside her, and guide her.” The television cameras pulled back and the surprised anchors grew quiet. On the steps, the voices of men and women, blacks and whites, Democrats and Republicans, rose together in unison: “Through the night with the light from above.” With fires still burning at the Pentagon just a few miles away, the song became huge: with pride, with tenacity, with sadness. “From the mountains, to the prairies,/ To the oceans, white with foam./ God bless America,/ My home sweet home.” It was a chorus that swept a nation, a truly United States of America, into a war to overthrow the Taliban regime in Afghanistan.

How things change. By 2010, many Americans saw the military campaign in Afghanistan as a futile endeavor. The layers of support for the war effort peeled away, one by one. Matthew Hoh, a State Department employee in Afghanistan, became the first senior official to resign in protest at the war. On September 10, 2009, he wrote that the families of Americans killed in action: “must be reassured their dead have sacrificed for a purpose worthy of futures lost, love vanished, and promised dreams unkept. I have lost confidence such assurances can anymore be made.” Conservative commentator George Will argued that the United States must end its hopeless nation-building mission in Afghanistan: “before more American valor … is squandered.”

In December 2009, President Barack Obama announced a new strategy in Afghanistan in a speech at West Point: “It’s easy to forget that when this war began, we were united-bound together by the fresh memory of a horrific attack, and by the determination to defend our homeland and the values we hold dear. I refuse to accept the notion that we cannot summon that unity again.” Obama was right. Americans will summon that unity again-just not in regard to Afghanistan.

How had it come to this? Why did we shift from singing “God Bless America,” to seeing America’s blessed valor being squandered in a futile quagmire? Perhaps the mission in Afghanistan was simply a disastrous failure. But what if our experience of hope and disillusionment in the Afghan War reflected something deeper in the American mind and in American history? What if we are characteristically predisposed to revel in the overthrow of an evil regime, and equally likely to see nation-building in Afghanistan as a grim and forbidding labor?

Sitting on the steps of the Lincoln Memorial in Washington, D.C., and looking toward the Capitol, where members of Congress gathered that night to sing, we can see America’s vision of how war is meant to be. Behind us is a marble Abraham Lincoln, enthroned in his temple, and flanked by the national hymns of the Gettysburg Address and his second inaugural address. Straight ahead lie the Reflecting Pool and the World War II Memorial. The shimmering water bridges America’s two “good wars”: the first to save the Union and free the slaves from 1861 to 1865, and the second to defeat fascism from 1941 to 1945. The fifty-six pillars and the giant arches of the World War II Memorial signify America’s common purpose, when the home front and the battle front united to crush evil. Anchoring the military vista, at the far end of the Mall, is a statue of Civil War general Ulysses S. Grant. On a platform of Vermont marble, Grant sits atop his horse, calm amid the fury of battle.

A triumphant tale unfolds before us, with World War II bookended by the Civil War titans, Lincoln and Grant. It’s a panorama of glory and victory, a narrative of liberation through force of arms: freedom born; global freedom redeemed. This is what war ought to look like: decisive victory, regime change, and the transformation of the world-a magnificent crusade. But if we broaden the view from the Lincoln Memorial, our peripheral vision reveals a less comfortable military narrative. Hidden away behind trees on the right-hand side is a memorial to the 1950-1953 Korean War. This was no splendid crusade. There was no decisive victory. There was no regime change or transformation of the world. Instead, the United States fought its opponents to a draw. For Americans, it was a bleak ordeal and a profoundly confusing experience.

The raw immediacy of the Korean War Veterans Memorial is utterly different from the abstract triumphalism of the World War II Memorial. The depiction of the Korean War focuses on the human experience of battle. A group of nineteen men, cast in stainless steel, slog their way uphill, sorrowful and exhausted, burdened with baggage and shivering under ponchos from the elements. The bushes and granite strips signify the rough terrain and horrendous conditions. We asked these men to fight in this environment, and they did.

Meanwhile, concealed under trees to the left is a testament to America’s tragedy in Vietnam from 1965 to 1973. This is what war ought not to look like. The United States spent years engaged in a futile nation-building effort in South Vietnam, trying to stabilize a weak government while battling a shadowy insurgency. With each step forward, Washington seemed to get further bogged down in the quagmire.

The Vietnam Veterans Memorial is a sunken black wall, inscribed with the names of the fallen. A knife cut into America’s body exposes a dark wound. To read the names of the dead, you have to physically descend into the gloom. Facing the wall, stand a group of U.S. soldiers, looking for something-perhaps their buddies, perhaps the meaning of this morass. The Vietnam Veterans Memorial does not commemorate the purpose of the war, but instead honors the sacrifice of the troops. There was no united home front to celebrate. In 1969, hundreds of thousands of demonstrators gathered on the Mall to protest against Vietnam in the largest antiwar rally in American history.

For soldiers and civilians alike, war is often a traumatic experience. It is bound up with our very identity. As a result, war is a subject of overwhelming interest, which has prompted the spilling of almost as much ink as blood. How do we unlock the puzzle of American thinking about this most emotive and critical of subjects?

The key is to distinguish between two types of military conflict: interstate war (where we fight against other countries) versus nation-building (where we fight against insurgents). Inspired by idealism and vengeance, we view interstate wars like World War II as a glorious cause to overthrow tyrants. I call this the crusade tradition. These same cultural forces, however, mean that we see nation-building in places like Vietnam or Afghanistan as a wearying trial, in which American valor is squandered. Whether the stabilization operation is a success or a failure in reality, we usually perceive it as a grim labor. I call this the quagmire tradition.

In other words, Americans are addicted to regime change and allergic to nation-building. In 2000, George W. Bush said: “I don’t think our troops ought to be used for what’s called nation-building … I think our troops ought to be used to help overthrow the dictator when it’s in our best interests.” This sentiment is as American as apple pie.

The type of war that we are comfortable fighting is very narrow. The enemy must be a state and not an insurgency. And we need to march on the adversary’s capital and topple the government. As soon as Washington deviates from this model, the glue binding together public support for the war effort starts to come unstuck. This insight explains why people back some conflicts but not others, how the United States fights, why Washington wins and loses, and how Americans remember and learn from war.

Many of us view each conflict in history as a distinct and unique event, with no overarching sense of how these campaigns relate to our past, and inform our future. But while America’s wars don’t repeat themselves, they do rhyme, producing a cadence in the nation’s encounter with battle. Crusades like the Civil War, the world wars, and the Gulf War, all follow a similar enthusiastic beat. Nation-building operations in Vietnam, Somalia, and Iraq hit the same weary notes.

If America’s military experience is an epic song, each verse has a predictable rhythm. When the first shot is fired, the public rallies around the flag. Crusading enthusiasm sweeps the nation until the great dictator is overthrown. But once the United States begins nation-building in a conquered land, hope quickly turns to regret.

We saw this pattern play out in Iraq. In the spring of 2003, the public was confident and supportive as U.S. forces raced to Baghdad to eliminate Saddam Hussein’s government. Then suddenly, the statue of Saddam fell, and Americans were in the midst of the greatest nation-building operation since Vietnam. As U.S. forces began fighting insurgents and overseeing elections, the entire tone of America’s thinking about the war changed. By 2007, tens of thousands were protesting on the Mall against the intervention in Iraq.

This is a critical moment to reflect on the nation’s experience of war. With fighting ongoing in Afghanistan and Iraq, Americans are trying to understand the new era of terrorism and counterinsurgency. The decisions that presidents make in the next few years may steer the course of U.S. foreign policy for generations.

The crusade and quagmire traditions have often served America well. The crusading instinct guided the United States to total victory in the colossal struggles of 1861 and 1941. Fears of a quagmire have sometimes deterred Americans from unwise interference in other countries’ civil wars.

But the world is rapidly changing. The end of the Cold War and 9/11 caused sudden seismic shifts, while globalization produces constant dynamism. The primary threats we face arise not from great powers such as Nazi Germany or the Soviet Union, but from the interconnected issues of terrorism, rogue states, failed states, and weapons of mass destruction.

In this environment, we must pursue military campaigns that do not fall within our blinkered view of idealized war, but rather in our peripheral vision of uncomfortable conflict. Modern technology is so destructive that we may need to avoid crusades and fight limited interstate wars, with restricted objectives that fall short of regime change. After all, we can’t always march on the enemy’s capital. And it’s almost certain that the United States will have to engage in nation-building to stabilize failed or failing states. This is the face of modern war.

But limited interstate war and nation-building seem un-American and are politically very difficult. We prefer smashing dictators, not dealing with the messy consequences. In Iraq, we are paying a terrible price for these attitudes. The failure to plan for post-conflict reconstruction proved catastrophic as the country descended into a vortex of looting and violence. Can we adapt to a changing world? For inspiration, Americans can look back through history. Our tendency to envision wars as either crusades or quagmires emerged at the time of the Civil War. Lost in popular memory is a very different military ethos that existed in the first years of the Republic. The earliest Americans did not demand expansive crusades to crush enemy tyrants. Instead, they favored restricted campaigns against other countries. And the Founders also supported the military’s involvement in nation-building, to develop the United States and open up the West to settlement. American soldiers dug canals and erected bridges. They built roads, dredged harbors, and explored and surveyed the land. They aided travelers heading west and offered relief to the destitute. The Founders created a multipurpose army designed for a wide range of challenges, and so should we.

This argument does not fit neatly into traditional categories. It’s not liberal or conservative. It’s not Democratic or Republican. It’s not hawkish, dovish, neoconservative, or isolationist. Rather, at a time when we face new threats and are divided by extreme partisanship, we need to uncover the hidden assumptions that guide our thinking and generate a fresh perspective on the vital questions of war and peace.

In the following chapters, we will travel from Gettysburg to Manila Bay, from the bloody killing fields of France to the improvised explosive devices in Iraq today. We will see the United States roused into a crusading fervor before falling into deep regret, only to be roused again. We will reflect on the ways that we remember war and how these memories take hold of us, how they awaken and limit our sense of the possible. Finally, we will turn to the founding generation and consider a very different vision of conflict.

The book draws on a wide range of literatures, on strategic culture, public opinion, psychology, idealism, and revenge. The sources include opinion polls, letters, poems, novels, memorials, newspapers, posters, photographs, country music, movies, Star Trek, and the engravings on Zippo lighters. But it’s not with a poll, or a letter, or a novel that we start. It’s with a speech, the words of which are etched into the Lincoln Memorial where we sit.

The book is available here: https://www.facebook.com/howwefight