AMERICA’S FOREIGN-POLICY difficulties are multiplying, from Asia to the Middle East. Faced with the prospect of losing in Afghanistan, the president on the recommendation of his military advisers (and reversing a previous stand) has announced a new, notably vague and apparently open-ended “strategy” that includes sending additional U.S. troops. And he promises to “win,” without really explaining how we will know if we have won.

In what has been called a “silent surge,” the administration is deepening American involvement in the endless conflicts raging across the Middle East and Africa. Relations with Russia have soured measurably, if not yet to the extent Trump’s hyperbolic rhetoric suggests. A full-fledged crisis with North Korea erupted in August and continues to smolder. And the president has even tossed about possible military intervention in Venezuela, an idea that anyone with even a scant knowledge of the history of U.S. relations with Latin America would not seriously entertain.

Coincidentally, we are “commemorating” the fiftieth anniversary of the Vietnam War, a conflict that dragged on for years and tore this nation apart. Throughout 2017, the New York Times online edition ran two articles a week on the war in 1967. Ken Burns and Lynn Novick’s television extravaganza aired in September, and a flood of new Vietnam-related books is hitting the market. Such significant anniversaries, particularly those involving national calamities, understandably invite reflection, in the hope that they may aid us in avoiding a repetition of the original error.

Each historical situation is unique; to extract “lessons” from one to apply to another can be at best misleading, and at worst disastrous. The so-called Manchuria/Munich analogy that helped draw the United States into Vietnam is a prime example. Former Kennedy adviser James Thomson once proclaimed, in reductionist words—containing a large grain of truth—that the central lesson from Vietnam should be never again to “take on the job of trying to defeat a nationalist anti-colonial movement under indigenous communist control in former French Indochina,” a lesson, he quickly—and redundantly—added, that was of “less than universal relevance.” History can be a treacherous teacher. Still, an understanding of some of the things that went wrong in our once-longest war (Vietnam) might help us deal with its successor (Afghanistan) and the myriad other problems we now face.

FROM EISENHOWER through Nixon, each new administration, certain that it was smarter and tougher, took power believing it could succeed in Vietnam where its predecessors had failed. We call this the certitude of the new guys. “We will not make the same old mistakes,” Henry Kissinger confidently announced upon taking office. “We will make our own.” In fact, like those who came before, the Nixon administration did make the same old mistakes—as well as plenty of new ones.

Trump personifies, and takes to another level, this new-guy mentality. He constantly bemoans the problems he inherited from the alleged failures of those incompetents who preceded him while, often with bombastic language, he promises to solve the problems they couldn’t.

It’s a little late for this one, perhaps, except that new guys continue to go through the revolving door that is the Trump White House. These newbies, and the president himself, no matter how smart and tough they think themselves, would do well to approach the problems they confront with humility and caution, especially those, like the president, who are totally lacking in foreign-policy experience and expertise. To be sure, they should learn from their predecessors’ mistakes, but they should keep in mind that they will make their own as well.

Another lesson from Vietnam so obvious as to be self-evident—easy in, not-so-easy out—has been ignored by perennially hubristic Americans from James Madison to George W. Bush. No one has stated it better than Lyndon B. Johnson, a year before he plunged into the quagmire by drastically increasing the number of U.S. combat troops in Vietnam. “It’s damn easy to get into a war,” LBJ told National Security Advisor McGeorge Bundy prophetically in May 1964, “but it’s going to be awful hard to ever extricate yourself if you get in.”

Given how frequently neoconservatives quote Winston Churchill in so many other contexts, it is striking that they don’t take to heart this particular admonition of his: “The Statesman who yields to war fever must realise that once the signal is given, he is no longer the master of policy but the slave of unforeseeable and uncontrollable events.” Former president Barack Obama took a lot of flak for winding down the U.S. military presence in Iraq in 2010. But given how hard it is to disengage from a major military commitment, the fact that he was able to do so at all is remarkable. The lingering U.S. commitment to Afghanistan, which President Trump now proposes to increase again, is more typical of the general pattern of easy in, not-so-easy out for major military commitments, even ones that are clearly not going to end well no matter how long we stay the course.

A THIRD lesson might be called the impotence of idle threats. Inasmuch as Richard Nixon had a “secret plan” for peace, as he claimed during the 1968 campaign, it was based on the so-called “madman theory,” a stratagem of persuading an enemy of one’s irrationality and then threatening the use of nuclear weapons to force a settlement. “They’ll believe any threat of force Nixon makes because it’s Nixon,” the candidate confidently told aide Bob Haldeman while strolling on the beach.

“We’ll just slip the word to them that, ‘for God’s sake, you know Nixon’s obsessed about Communism . . . and he has his hand on the nuclear button’—and Ho Chi Minh himself will be in Paris in two days begging for peace.”

Nixon’s madman approach drew upon the mistaken belief, an article of faith among some Republicans, that Eisenhower had forced the Chinese to settle in Korea in 1953 by making nuclear threats. It also derived from academic studies of “diplomatic blackmail” developed by the economist Thomas Schelling and, ironically, by Nixon’s future nemesis, Daniel Ellsberg.

Nixon’s madman diplomacy failed. Through various sources, he warned Hanoi in the summer and fall of 1969 that if a settlement were not reached by November 1 he would resort to “measures of great consequence and force.” His threats were singularly ill timed. Ho Chi Minh died in September, and the hard-liners who had long since supplanted him were not about to dishonor his cause by giving in to the United States. Those Nixon officials tasked to devise a military program to coerce North Vietnam concluded that nothing was likely to work, and that drastic escalation would bear a high domestic political cost.

It would be natural for anyone assuming the American presidency to be awed by our military power. It is human nature to believe that small nations, even ones with nuclear weapons, can be easily cowed by Mr. Big. In fact, as various presidents have discovered, there are numerous powerful internal and external constraints on the use of the nation’s vast power. And hard experience should have taught us by now that other nations and peoples, however small and seemingly weak, are not easily intimidated.

Another cautionary “lesson” from Vietnam is to resist the temptation of quick-fix strategies—in football lingo, the Hail Mary pass. In the run-up to massive U.S. involvement in Vietnam, decisionmakers like Assistant Secretary of Defense John McNaughton, already doubtful that military intervention would compel North Vietnam to stop aiding its southern allies, sought a Hail Mary pass in the theories of coercive bombing developed by Schelling, his friend and former Harvard colleague. In late 1964, working with the State Department, McNaughton devised a bombing campaign of graduated pressures against North Vietnam that he hoped would achieve U.S. goals and avert a disaster in Vietnam. “What we need is a theory that will limit our role,” he confided to his diary.

Schelling’s model and the Rolling Thunder air campaign that drew upon it erroneously assumed the same cost/benefit calculations on both sides. In fact, the United States sought merely to demonstrate its resolve to allies and enemies; North Vietnam sought to liberate what it considered its homeland. Rolling Thunder evolved into a prolonged, vastly destructive and ultimately futile exercise in coercion.

The Trump administration, similarly, faces a set of bad choices in Afghanistan. Setting aside his own well-founded instincts against escalation, the president was persuaded by his top advisers that a hasty withdrawal would create a vacuum for terrorists such as ISIS and Al Qaeda. Like McNaughton, and Trump’s predecessor, Barack Obama, he succumbed to the lure of the quick fix in the graveyard of empires. Hail Mary passes rarely win football games. Why should we expect them to win wars?

IN VIETNAM, both U.S. president Lyndon Johnson and his North Vietnamese counterpart, party general secretary Le Duan, repeatedly miscalculated how each would respond to the other’s initiatives. In escalating the war in 1965, Johnson and his advisers assumed—incorrectly—that North Vietnam would acquiesce to an independent South Vietnam rather than risk destruction at the hands of America’s vast military power. In 1964, and again in 1968 and 1972, the aggressive—and reckless—Le Duan assumed that he could win in South Vietnam by drastically escalating the war. In each case he failed, and in so doing he imposed horrendous costs on his people and nation.

Miscalculation lies at the root of many, if not most, foreign-policy crises and wars. Trump and his advisers should be very careful about what they say and do, and especially about what they assume about the possible behavior of enemies both real and potential. War and peace is not a schoolyard game of one-upmanship. It is, literally, life and death.

IN VIETNAM, too, we became entangled in what one top official (with no apparent sense of the paradox) called an “all-out limited war” through a series of decisions made over almost two decades. With each step out on the slippery slope, from aid to advisers to more advisers to combat troops, we became more deeply committed until that commitment itself—our credibility—became the essential reason for further, massive escalation.

The dangers of incrementalism certainly apply today in places like Afghanistan and Iraq, where our commitment is limited to advisers whose numbers and roles may soon be expanded. How, after sixteen years, can we continue to believe that a small—or even a large—infusion of U.S. troops in Afghanistan can do what more than one hundred thousand could not previously accomplish? At what point do we decide that even a major commitment of Americans cannot compensate for the weakness of our ally?

Of course, with Trump, as with Barack Obama and George W. Bush, domestic politics likely influenced decisions to up the ante in Afghanistan. No one wants to see that country “lost” on his watch. This is eerily reminiscent of what Ellsberg called the “stalemate machine” in Vietnam, with each president doing just enough to keep South Vietnam afloat until he leaves office.

CLOSELY RELATED is a geopolitical truth that Americans historically have been loath to accept—that power, no matter how great, has limits. In the 1960s, the United States was the world’s greatest power militarily and economically, but in Vietnam it could never find ways to use that power to attain its political goals of thwarting North Vietnamese expansion and building, from scratch, a Jeffersonian democracy in the South.

We still enjoy a vast advantage over other nations in military spending and hardware. No more than in the Vietnam era does that mean we can solve the problems we face on terms we favor. Our power greatly exceeds our capacity to use it.

Americans tend to believe that what they do—or don’t do—is the key to success or failure in foreign policy. In fact, as Vietnam showed so clearly, local circumstances often determine outcomes.

A weak, divided South Vietnam proved so unreliable as an ally that after 1965 we tried to do the job of defeating the North almost on our own. At the same time, our resolute, utterly committed foes, the National Liberation Front (Viet Cong) and North Vietnam, were the ones in fact willing, in JFK’s words, to “pay any price, bear any burden” in pursuit of victory. They had sanctuaries to protect themselves from extermination, and allies like China and the Soviet Union to provide massive assistance.

In Afghanistan today, we back a weak, corrupt central government in a vast nation with no tradition of federal control and a small scattered population divided along ethnic, religious and tribal lines, surrounded by nations with more compelling interests and greater ability than the United States to affect the outcome—while fighting against a resilient foe that seems magically to recreate itself after each setback, enjoys sanctuaries in Pakistan that help it to do so and possesses infinite patience. Can the application of our power make up for these intrinsic disadvantages?

Both then and now, American leaders have failed to know their enemies. LBJ longed to get “ol’ Ho” Chi Minh in a room where he could employ his formidable powers of persuasion, in the mistaken belief that Ho was no different from the labor leaders and legislators he was accustomed to manipulating. Ho was not a senator or labor leader, of course, and even if LBJ had gotten him in a room, he likely could not have persuaded him to compromise on American terms.

Most alarming is that U.S. leaders apparently had no idea that after 1963 at the latest, Ho did not wield dominant power in Hanoi. In fact, the pragmatic Ho’s earlier compromises with the French in 1946 and at the Geneva Conference in 1954—his “two mistakes”—had become by 1965 for Le Duan and his hawkish allies a compelling mantra against any compromise with the United States that in any way undermined the fundamental goal of a unified Vietnam under Hanoi’s control.

In dealing with our Middle East adversaries—and China, Russia and especially North Korea—President Trump ought not to assume that they will respond to his bluster and blandishments in the same way partners and rivals in the business world did. Rather, the art-of-the-dealer in chief needs to recognize that other countries have their own history and perspectives on the contemporary world that may, or more likely may not, accord with his, and that getting to “yes” with them may require very different tactics than those he used to build his real-estate empire.

The admonitions recounted here undoubtedly appear weighted on the side of nonintervention or limited intervention. But these lessons are bipartisan. They are grounded in important premises of both conservative (prudence) and liberal (humility) political thought. Given America’s dismal record in the past few decades, such restraint appears prudent—and greater national humility about our role in the world appears eminently justified.

George C. Herring is Alumni Professor of History Emeritus at the University of Kentucky. Michael C. Desch is professor of political science and founding director of the Notre Dame International Security Center.

Image: President Lyndon B. Johnson in Vietnam, 1966. Wikimedia Commons/Public domain