Today, nearly nine out of ten wars are civil wars. For Washington, foreign internal conflicts have become a major security challenge, producing humanitarian crises, refugee flows and terrorism. The 2002 National Security Strategy asserted, “America is now threatened less by conquering states than we are by failing ones.”

THE RISE of alien warfare has severely eroded America’s performance on the battlefield. If we define victory as the achievement of core aims with a favorable ratio of costs and benefits, before 1945, the United States won most of its major wars. The War of 1812 returned the belligerents to the prewar status quo and can be classified as a draw. The bloody suppression of the guerrillas in the Philippines was also an ambiguous outcome. Meanwhile, the Mexican-American War, the Civil War, the Spanish-American War, World War I and World War II can all be counted as U.S. military successes. The costs of these campaigns were sometimes staggering, with around 750,000 American fatalities in the Civil War alone. But the benefits were also colossal. The Civil War saved the Union and emancipated the slaves. World War II ensured the survival of liberal democracy in Western Europe. Therefore, the overall tally from 1812 to 1945 is five victories, two draws and no defeats.

By contrast, since 1945, most major U.S. wars have ended in stalemate or defeat. Washington achieved a successful outcome in the Gulf in 1991. Korea, however, was a grim stalemate, in which nearly thirty-seven thousand Americans died to restore the prewar status quo. Cartoonist Bill Mauldin called it “a slow, grinding, lonely, bitched-up war.” Vietnam was an even more punishing experience, where the United States faced outright military defeat for the first time in its history. Despite the deaths of fifty-eight thousand Americans, South Vietnam still fell to Communism.

In 2001, the United States swept aside the Taliban regime in Afghanistan. But the Taliban recovered, setting the stage for today’s stalemated conflict. After a dozen years of tough fighting, with over two thousand Americans killed and twenty thousand wounded, and the expenditure of hundreds of billions of dollars, the campaign has been far too costly to be considered a success.

Meanwhile, the Iraq War was a clear failure. The conflict killed 4,500 Americans, injured over thirty thousand, presented Al Qaeda with a new battlefield, strengthened Iran by removing its nemesis Saddam Hussein, and triggered a spike in anti-Americanism. Overall, the United States has only won one of its five major wars since 1945.

The combination of culturally unfamiliar environments and sustained nation building and counterinsurgency proved toxic. The first problem is that Americans do not understand the local country. Washington often projects a simplistic global image onto complex regional conflicts. During the Cold War, U.S. officials saw Communism as monolithic and Vietnamese leftists as mere pawns of Moscow and Beijing. But Vietnam has resisted Chinese influence for two millennia. After Vietnam unified in 1975, Vietnam and China soon went to war.

Similarly, the George W. Bush administration lumped Iran, Iraq and North Korea together into an “axis of evil” despite the lack of any real alliance between these states. Meanwhile, the “war on terror” frame presented Al Qaeda and the Taliban as fundamentally identical, even though Al Qaeda’s goals are international and revolutionary whereas the Taliban’s goals are mainly restricted to Afghanistan and Pakistan.

Furthermore, U.S. soldiers were strangers in a strange land. Cultural incomprehension was a much greater problem for the United States in counterinsurgencies than in interstate wars. When Washington fights an unfamiliar country, like Japan in World War II, mutual misunderstandings produce errors on both sides that may cancel themselves out. The Japanese thought that Americans lacked the necessary resolve to win. U.S. troops were told the Japanese were half-blind and could not fight. On balance, neither side benefited from these mistakes.

But when Washington wades into a distant civil war, cultural differences damage the United States far more than the insurgency. The two sides battle for the loyalty of the people, but the rebels understand this prize much better than the Americans. The United States needs accurate intelligence to separate the guerrillas from the people. Washington, however, has limited knowledge of local social dynamics.

In South Vietnam, for example, Washington attempted an ambitious nation-building program, which involved creating a civil service; building hospitals, roads and telecommunications; and training police. But, as Frances FitzGerald described, there was a culture clash between the individualistic and capitalist West and the communal Confucian-Buddhist Vietnamese. U.S. soldiers “knew everything about military tactics, but nothing about where they were or who the enemy was.” Senator J. William Fulbright said Westerners were “alien to their culture, and where the French failed, we will fail.”

The second problem with alien warfare is that the local people do not understand Americans. For the indigenous population, Americans are the aliens. U.S. soldiers descend from nowhere and start reordering their society. America’s destructive machines of war may seem like the Martian tripods in H. G. Wells’s War of the Worlds. Armed to the teeth and shouting in a strange tongue, American soldiers can be a terrifying sight. U.S. intervention may provoke an antibody response as the local people rally against the threatening intruder, creating what counterinsurgency expert David Kilcullen called “accidental guerrillas.”

Alien warfare runs headlong into the most powerful political force in modern history: nationalism. The idea that every nation should decide its own fate free of external compulsion is now widely accepted—and is even inscribed into the UN Charter. After 1945, national self-determination was the insurgents’ ace card. During the Cold War, Communist insurgents combined nationalism and Marxism in a “national liberation movement.” More recently, the Taliban fused together nationalistic appeals against the foreign occupier with calls for stricter forms of Islam. As the United States found in Vietnam, trying to hold back the tide of nationalism can be a futile endeavor.

The third problem with alien warfare is that Washington failed to adapt to the new era of conflict. In conventional interstate wars, the United States developed a playbook for victory: overwhelm enemy countries with mass production, logistics and technology. At its peak capacity in World War II, American industry churned out a new aircraft every five minutes and forty-five seconds.

After 1945, U.S. military campaigns shifted from interstate war to counterinsurgency, but Washington clung to the same set of tactics. William Westmoreland, the U.S. commander in Vietnam, said the solution to the insurgency lay in one word: “Firepower.”

This approach, however, proved disastrous in civil wars. Counterinsurgency is a different kind of campaign from interstate war and requires a specific skill set. Defeating guerrillas means winning hearts and minds, developing networks of human intelligence and enhancing the legitimacy of the host regime. Indiscriminate firepower causes collateral damage and may create more enemies. One study, for example, found that areas of South Vietnam bombed by the United States tended to shift over to insurgent control.

During the early years of the Iraq War, Washington also failed to follow the basic principles of counterinsurgency theory. The George W. Bush administration pursued a “small footprint” invasion plan that lacked sufficient troops to stabilize the country following regime change. U.S. soldiers hunkered down in forward operating bases far removed from the Iraqi people. With too few forces to permanently clear areas of insurgents, and with American troops isolated from the Iraqi people, violence quickly escalated.

THE EMERGENCE of alien warfare also undermined Washington’s ability to negotiate effectively with opponents. Given America’s struggles on the battlefield, it often became imperative to parley an end to war. But cultural unfamiliarity triggered prolonged and frustrating negotiations in Korea, Vietnam and Afghanistan.

The peace talks that resolved the War of 1812 were a model of civility. The British and American negotiators met in Ghent, in modern-day Belgium, in the fall of 1814. They all spoke the same language. The British offered to meet the Americans at their hotel but the Americans preferred to talk at the British residence. By December 1814, the discussions were wrapped up and the two sides agreed to return to the prewar status quo.

Since 1945, negotiating an end to deadlocked wars has proved to be far more tortuous. From 1951 to 1953, Washington spent two years discussing a truce in Korea, even as brutal attritional fighting continued. An armistice was eventually signed in 1953, but the negotiators barely even acknowledged each other’s presence. According to the London Times, “There was no pretense at an exchange of courtesies, or even of civility.”

When negotiations began to resolve the Vietnam War in 1968, the U.S. diplomatic team made hotel reservations in Paris for a week. By contrast, the North Vietnamese leased a chateau for a year, and said they would sit in Paris until the chairs rotted. In the end, the Communists were more realistic about the timescale, as the talks dragged on until 1973.

Negotiations in Afghanistan have been a similarly wearying tale. For a decade after the fall of the Taliban in 2001, the opposing sides barely talked to each other. Washington was unwilling to engage the patrons of Al Qaeda. The Taliban refused to negotiate directly with Kabul, and labeled Hamid Karzai as a puppet of the United States. In 2010, Karzai appointed Burhanuddin Rabbani as chair of the High Peace Council, with a mandate to engage the rebels, but the insurgents killed him with a suicide bomber.