The war in Iran is far from the first time that U.S. policymakers have failed to appreciate the limits of American power. But the Trump administration’s use of military force against the Islamic Republic since February 28 offers a particularly glaring example of a mistake that has often characterized American strategy in recent decades. The war was launched without a clear rationale and with a constantly shifting set of objectives—from changing Tehran’s regime and squelching its nuclear ambitions to, more recently, reopening the Strait of Hormuz, which wasn’t closed until the war started. The results, not surprisingly, have been bad both for U.S. interests and for the Middle East.

Still, to focus only on the blunders in Iran is to miss a deeper problem in U.S. foreign policy—one that preceded and will outlast Donald Trump’s presidency. Although the particular missteps in Iran may stem from the shortcomings of this president and the team around him, the overestimation of the potential of military force has been a growing feature of American strategy since at least the end of World War II. A tendency to wish away the limits of power accounted for some of the greatest mistakes of U.S. statecraft during the Cold War, with Vietnam the clearest and most consequential example. Yet despite an apparent commitment to internalizing the lessons of that overreach, this American delusion—our excessive faith in the capacity of military power to achieve victory and thereby fundamentally political ends—has gotten worse rather than better, especially in the past quarter century.

And unfortunately, there is good reason to worry that the delusion will deepen in the years ahead. Presidential power is becoming increasingly personalized as the constraints on it continue to erode. The politicization of the military (along with the diplomatic corps and intelligence communities) is making it less likely that policymakers will receive the best advice, including frank warnings about risks and costs. And the rise of artificial intelligence and new weapons technologies reinforces a sense of complete battlefield awareness and mastery, feeding superpower hubris. The risk of overreach has never been higher, at a time when the damage from overreach is becoming more difficult to repair.

In April 1975, Colonel Harry Summers, a member of the U.S. delegation dealing with postwar issues in Vietnam, was meeting in Hanoi with a North Vietnamese counterpart, Colonel Tu. “You know, you never defeated us on the battlefield,” Summers observed. To which Tu replied, “That may be so, but it is also irrelevant.”

Summers went on to write a seminal book about the war, On Strategy: A Critical Analysis of the Vietnam War. His key takeaway was simple: there are limits to American power that are neglected at immense cost. War is, and always has been, a contest of human will, shaped by heroism and cowardice, fear and elation, chance and uncertainty; no matter how superior a military force, it is not guaranteed strategic victory.

The book became required reading for many military officers, including me. I had joined the Naval ROTC unit at the University of Texas two years before the encounter between Summers and Tu. The draft had just ended, and the fall of Saigon was still to come, but discussion of Vietnam consumed our ranks. As I studied the American failure, I came to see that a great strength had become a fatal liability: our fundamental faith that we, the United States of America, had to win and thus would. We had won World War I, we had won World War II, and we had at least fought to a draw, holding off the North Koreans and Chinese, in Korea. And somehow, at all costs, we would win in Vietnam.

To believe you can win is important. It inspires troops and keeps the public engaged. But when the commitment to winning is not coupled with sound policy judgment, when the principles of war are disregarded in the false belief that technology or firepower can overcome the inherent frictions of combat, when tactical successes are viewed as a guaranteed path to a strategic win, when the cost in blood and treasure rises inexorably while any claim to righteousness collapses, it is essential to reassess. In Vietnam, the answer to mounting losses was simply “more”—more troops, more bombs, more money. To lose the fight was seen as anathema to all we stood for; we would keep fighting in spite of the increasingly evident limits to our power. When the end finally came with the rushed U.S. withdrawal from Saigon in 1975, many military and political leaders could still not understand how the United States had won nearly every skirmish, battle, and fight but lost the war.

The damage from overreach is becoming more difficult to repair.

The military I entered in 1977 was struggling in the aftermath of Vietnam. The “peace dividend” meant a dramatic drawdown in manpower and money. Readiness was at an all-time low across the services—army enlistment had fallen by 60,000 and the number of navy ships from around 650 to barely more than 500. Meanwhile, the transition to an all-volunteer military had proved challenging: drug abuse and racial tensions were high, morale among senior leaders and young troops alike was low, and new recruits lacked basic skills.

When President Ronald Reagan took office in 1981, he began the largest peacetime expansion of the U.S. military since the Korean War. Over the course of eight years, he increased defense spending by 35 percent. There was a slew of major procurements: the M-1 Abrams tank, the Bradley Fighting Vehicle, the Apache and Black Hawk helicopters, the F-15 and F-16 fighters, the B-1 bomber, the E-3 Sentry. The navy built back toward 600 ships, including 15 aircraft carriers, 100 attack submarines, and cruisers and destroyers equipped with the revolutionary Aegis Combat System. For troops, pay rose, recruiting goals were met, and standards were restored. Just as important, Congress passed the Goldwater-Nichols Act in 1986. It fundamentally changed the military by strengthening the role of the chairman of the Joint Chiefs of Staff, establishing the regional combatant commanders as the warfighters, ensuring joint force integration, improving joint planning and procurement, and leading to the establishment of the U.S. Special Operations Command. By 1990, the military I entered in the 1970s had been transformed. Our troops were well trained, well equipped, highly motivated, and, most important, well led.

In July 1990, I left San Diego on a routine six-month deployment to the western Pacific. I was a SEAL task unit commander assigned to Amphibious Squadron Five and the 13th Marine Expeditionary Unit. Little did I know that this reinvigorated military and our civilian leaders were about to be tested, raising the question of whether the United States had learned anything from Vietnam and the other failed missions of the recent past.

On August 2, 1990, Iraqi President Saddam Hussein ordered the Iraqi army into Kuwait. Within hours of the invasion, the National Security Council convened and options for U.S. action were presented to the president. “This is the first test of the postwar system—as the bipolar world is relaxed, it permits this,” Deputy Secretary of State Lawrence Eagleburger emphasized. “If [Saddam] succeeds, others may try the same.”

Fortunately, American leadership had never been stronger or more experienced—and in wartime especially, leadership matters. President George H. W. Bush was a young navy pilot when he was shot down near Iwo Jima and eventually rescued by an American submarine. Bush understood war. Later in life, he had served as U.S. ambassador to the United Nations, de facto ambassador to China, director of the Central Intelligence Agency, and vice president. No president in American history had come into office with more national security experience. Nevertheless, Bush surrounded himself with some of the most remarkable diplomats, military officers, intelligence professionals, and strategic thinkers........

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