The reductio ad absurdum, as dialecticians of all stripes will tell you, is a simple and elegant way to disprove a false proposition. Assume the proposition is true, then begin deriving conclusions from it; if one of them is obviously absurd, then the original proposition must be false.

I have spent the past forty-five years investigating the origins of wars, and time and again my research has led back to this concept. Nations often go to war based on seemingly logical (and popular) principles—yet the attempt to apply those principles leads only to disaster, leaving the warlike power worse off than it was when it began, even with respect to the specific goals for which the war was undertaken. The United States has been replaying this drama in Afghanistan. But before I explain why, let me review three earlier such cases.

 The first involves Athens. Two and a half millennia ago, shortly after the Peace of Nicias temporarily halted the Peloponnesian War between Athens and Sparta, a delegation of Athenian colonists from Egesta, in Sicily, came to Athens to ask for help against the leading power of that island, Syracuse. Thucydides tells us that the majority favored the expedition as another means of adding to the great Athenian Empire. Nicias himself, however, argued that the peace he had negotiated was already fragile enough, and that Athens had not yet restored its rule over its existing empire. He was overruled, and the Athenians sent a massive expedition—an adventure that ended in utter disaster, sparking revolts all over the Athenian empire, the resumption of war with Sparta, and, in 404 BC, total defeat.

  Similar disaster beset Germany just last century, when twice within twenty-five years it pursued the dream of creating an empire to rival those of the British, the Americans, and the Soviets—and succeeded only in triggering war with all three. Those two global conflicts left Germany completely defeated and destroyed. Finally, here in the United States in 1964, the Johnson administration decided that the defense of South Vietnam was vital to American credibility abroad, ignoring warnings from the American diplomat George Ball that the attempt would fail and would in fact undermine our credibility. Eight years of war in Vietnam did that and more, opening wounds from which the country still has not recovered. (Ironically, our defeat in Vietnam probably did more to help our standing abroad than any victory could have, because it made it politically impossible for a U.S. president to conduct any large-scale foreign military adventures from the middle 1970s until the first Gulf War.)

 Now to Afghanistan. As Andrew Bacevich pointed out in these pages (“The War We Can’t Win,” August 14, 2009), the Bush administration decided in 2001 that post-9/11 security required the overthrow of the Taliban in Afghanistan for having sheltered Osama Bin Laden and his Al Qaeda training camps. The subsequent decision to overthrow the government of Iraq was presented as a first step toward the democratization of the Middle East—a process that, Bush argued, would make terrorism a thing of the past. As everyone now knows, the invasion of Iraq not only reduced that country to anarchy and civil war, but also allowed Al Qaeda to entrench itself in Iraq, where it had never previously been a factor. Meanwhile, the Taliban, initially driven into Pakistan, have had a major resurgence in the east and south of Afghanistan, and intermittently carry out attacks in Kandahar and Kabul.

 Official U.S. policy—to eliminate Taliban power and transform Afghanistan into a functioning state ruled by law—is based on a series of fictions. The first is that the Taliban and Al Qaeda are closely allied. In truth, the Taliban are an ethnic movement, composed almost entirely of Pashtuns, whose homeland straddles the Afghan-Pakistani border. And while they did form a temporary alliance with Al Qaeda, we now know—thanks to a study of captured laptops and documents by the Combating Terrorism Center at West Point—that Al Qaeda leaders, who have consistently made more enemies than friends wherever they have set up shop, were feuding bitterly with the Taliban before 9/11. Indeed, the real basis for any alliance between these groups today is the U.S. presence in Afghanistan. The Taliban themselves have never envisioned being more than a local threat, limited to the mountainous, remote, and poverty-stricken regions in which the Pashtuns live. I doubt any serious student of Afghanistan sees much chance of their taking control of the whole country; and in any case, the elimination of the Taliban as a power in Afghanistan, even if it could be achieved, would at this point have little impact on Al Qaeda, which has found other havens in Pakistan, Yemen, and parts of Africa.

 The second fiction is that Afghanistan is a country with an elected government whose sovereignty we are trying to help establish. In truth, Afghanistan has not been a united country for decades, not even under the Taliban’s five-year rule. And our attempt to establish democracy there seems to have proved mostly that the country isn’t ready for it. The United States adopted Hamid Karzai to represent its interests for the same reason it adopted Ngo Dinh Diem in Vietnam or Achmed Chalabi in Iraq: each was in the right place at the right time. A member of a Pashtun clan allied with the Mujahedeen in the fight against the Soviets, Karzai had fallen out with the Taliban and was living across the border in Pakistan in 2001, eager to enlist NATO and the United States to overthrow them. Like Diem, he relies heavily on a younger brother, Ahmad Wali Karzai, who reportedly has a continuing relationship with the CIA and is widely thought to be a major player in the drug trade. Corruption and ineffectiveness have made his regime so unpopular that Karzai had to rig his re-election last fall, shredding his credibility at home. Yet he is the man we are now defending against the Taliban with about fifty thousand troops—a figure scheduled to increase to eighty thousand by the end of this year.

 In a replay of Vietnam, our sponsorship of Karzai, like our patronage of Diem (and, later, Nguyen Cao Ky and Nguyen Van Thieu), seems more likely to weaken our credibility than to increase it. A devastating cable published by the New York Times revealed U.S. Ambassador Karl Eikenberry complaining that Karzai expects U.S. forces to stay in Afghanistan indefinitely, even as he “continues to shun responsibility for any sovereign burden, whether defense, government, or development.” Afghanistan, Eikenberry added, crucially lacks “an overarching national identity that transcends local affiliations and provides reliable partnership.” Even worse, it appears that significant amounts of the aid we are pouring into the country are falling into the wrong hands. A recent article by Aram Roston in the Nation detailed how the United States depends on local contractors to move supplies around the country—and how many of these contractors are suspected of paying off the Taliban themselves.

 The most absurd aspect of our policy involves Pakistan. One ostensible reason we are fighting the Taliban in Afghanistan is to deter them from becoming a threat in Pakistan. Unlike the U.S. government, however, the Pakistani government has always accepted the remote regions on both sides of its Afghan border as essentially ungoverned spaces. And what no one wants to talk about in public is that important elements in the Pakistani government and its intelligence service want the Taliban back in power in Afghanistan, viewing them as a useful ally against Indian influence. At the same time, the Pakistanis value our aid, which is reaching annual levels comparable to what we give the Egyptians and Israelis. And so their government walks a tightrope, confronting a new Taliban threat to itself fueled partly by U.S. drone strikes in the frontier regions, without doing very much to support U.S. goals on the other side of the border. Pakistanis find it advantageous to show some cooperation with the United States—but that cooperation has created an important Taliban insurgency against the government of Pakistan itself. It is not at all clear that this would have happened had the Taliban remained in power in Kabul. Meanwhile, rather than acknowledge that U.S. and Pakistani goals in Afghanistan differ, both American civilian and military leaders are parroting the Pakistani government’s argument that the United States has to prove itself a reliable partner after having imposed sanctions on Pakistan in the 1990s in response to its nuclear test.

 Building on the Iraq “surge” model, General Stanley McChrystal and his superior, General David Petraeus, now think the United States can successfully apply a “counterinsurgency” strategy in Afghanistan. In my opinion, the more accurate word is “occupation.” Counterinsurgency, a strategy employed by an established government to defeat a rebellious minority, does not describe either the situation in Iraq in 2007 or that in southern and eastern Afghanistan now. In Iraq, U.S. troops stationed in Sunni areas managed to cooperate with Sunni elites to eliminate much of Al Qaeda and stabilize the situation—at least for as long as U.S. troops remain. Afghanistan will be much harder to deal with. It is overwhelmingly rural, with few roads, and poses immense logistical problems. Stationing troops within certain Afghan towns and villages could help build up relationships with local elites and keep the Taliban away; but because the affected area of Afghanistan has thousands of villages, and because the Taliban will never lack for places to hide, it is very hard to see how a U.S. occupation can achieve lasting political results unless we stay forever—which of course we will not. Long-term success will remain hostage to a weak, fragmented, and corrupt local government. Meanwhile, dedicated and capable American troops will continue to suffer casualties from IEDs—and our large-scale occupation of another Muslim country will continue to provide a talking point for Islamist propaganda all over the world. Domestically the war will inflate our budget deficit and make the president’s ambitious domestic agenda much more difficult to achieve.

 The neoconservative argument that Islamic extremism, like communism, must be fought wherever it appears invites us to repeat some of the biggest mistakes of the Cold War. In 1948, arguing against increased aid to Nationalist China, Secretary of State George Marshall—one of our greatest statesmen—bluntly rejected the idea that the United States could or should intervene to counter any Soviet move anywhere in the world. Such a policy, he said, would cede all initiative to the enemy and force us to fight in places of its choosing. Following this principle, the United States should restrict its attention to Islamic extremism within the West itself, along sea lanes, and—perhaps—in economically important regions. Afghanistan fails all three of those tests.

 Though President Barack Obama has ordered thirty thousand additional troops to Afghanistan, some signs indicate that he and other officials are still re-evaluating our grandiose objectives there. Last December, Rajiv Chandrasekaran of the Washington Post reported that unnamed senior civilians, along with Vice President Joe Biden, disagreed with the Pentagon over exactly what the president had decided, insisting that merely holding on to Afghanistan’s major cities, not defeating the Taliban, was the goal. Meanwhile, some military commanders in Afghanistan are trying to deal directly with local tribal commanders, bypassing the Karzai government. And reports suggest that Hamid Karzai himself would like to talk peace with the Taliban—just as some South Vietnamese leaders in the 1963–65 period wished to pursue a settlement with the Viet Cong. Last month, the New York Times reported Pakistani government interest in mediating between the Taliban and the United States.

 All of this is welcome; scaling back our objectives would be a step in the right direction. Even so, it remains unclear to me how any American presence in Afghanistan is making the United States safer. Nearly nine years after 9/11, we have not apprehended those responsible, as Osama Bin Laden recently reminded us in a new broadcast to the world. Were I secretary of state, I would go to Islamabad and tell the Pakistani government we’re more than willing to wind down our involvement in Afghanistan quickly and halt drone strikes in Pakistan—provided they locate Bin Laden and his chief lieutenant Al-Zarqawi and hand them over for trial. Such a deal would be a major propaganda coup and enable us to focus on antiterror intelligence and domestic border security, rather than endless attempts to transform vast Muslim countries into friendly outposts of democracy.

 In my youth, the war in Vietnam convinced me that the United States serves both itself and others best by allowing other countries, to the maximum extent possible, to work out their own problems. Nothing that has happened in Iraq, Afghanistan, or Pakistan since 9/11 has changed my mind. When our country does otherwise, it risks being reduced again and again to absurdity, or worse.

Related: Read more of our Afghanistan coverage here.