New Rules for U.S. Military Intervention

September 20, 2016

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Editor’s Note: Welcome to the tenth and final installment in our new series, “Course Correction,” which features adapted articles from the Cato Institute’s recently released book, Our Foreign Policy Choices: Rethinking America’s Global Role. The articles in this series challenge the existing bipartisan foreign policy consensus and offer a different path.


Any nation with vast power will be tempted to use it. In this respect, the United States is exceptional because its power is so immense. Small, weak countries avoid fighting in distant disputes; the risk that troops, ships, or planes sent elsewhere will be unavailable for defense of the homeland generally keeps these nations focused on more proximate dangers. The U.S. government, by contrast, doesn’t have to worry that deploying U.S. forces abroad might leave America vulnerable to attack by powerful adversaries.

There is another factor that explains the United States’ propensity to go abroad in search of monsters to destroy: Americans are a generous people, and we like helping others. We have often responded favorably when others appeal to us for assistance. Many Americans look back proudly on the moments in the middle and latter half of the 20th century when the U.S. military provided the crucial margin of victory over Nazi Germany, Imperial Japan, and the Soviet Union.

But, in recent years, Americans have grown more reluctant to send U.S. troops hither and yon. There is a growing appreciation of the fact that Washington’s willingness to intervene abroad – from Somalia and the Balkans in the 1990s, to Iraq and Afghanistan in the 2000s, to Libya and Yemen in the present decades – has often undermined U.S. security. We have become embroiled in disputes that we don’t understand and rarely can control. Thus, public anxiety about becoming sucked into another Middle Eastern civil war effectively blocked overt U.S. intervention in Syria in 2013, notwithstanding President Obama’s ill-considered red line warning to Bashar al Assad.

But while the American people are unenthusiastic about armed intervention, especially when it might involve U.S. ground troops, most Washington-based policy elites retain their activist instincts. They believe that U.S. military intervention generally advances global security and that the absence of U.S. leadership invites chaos. The essays in this series, “Course Correction,” have documented the many reasons why these assumptions might not be true. The authors have urged policymakers to consider other ways for the United States to remain engaged globally – ways that do not obligate the American people to bear all the costs and that do not obligate U.S. troops to bear all the risks.

But the authors do not presume that the United States must never wage war. There are indeed times when it should. Policymakers should, however, keep five specific guidelines in mind before supporting military intervention, especially the use of ground troops. Doing so would discipline our choices, would clearly signal when the U.S. military is likely to be deployed abroad, and could empower others to act when the United States does not.

Vital U.S. National Security Interest at Stake

The United States should not send U.S. troops into harm’s way unless a vital U.S. national security interest is at stake. Unfortunately, the consensus in Washington defines U.S. national security interests too broadly. Protecting the physical security of the territory of the United States and ensuring the safety of its people are vital national security interests. Advancing U.S. prosperity is an important goal, but it is best achieved by peaceful means, most importantly through trade and other forms of voluntary exchange. Similarly, the U.S. military should generally not be used to spread U.S. values, such as liberal democracy and human rights. It should be focused on defending this country from physical threats. The military should be poised to deter attacks and to fight and win the nation’s wars if deterrence fails.

The criterion offered here is more stringent, for example, than the Weinberger-Powell Doctrine, which held that U.S. troops should not be sent overseas “unless the particular engagement or occasion is deemed vital to our national interest or that of our allies.” By effectively equating U.S. national interests with those of our allies, it allowed for a range of interventions that would not be considered automatically valid under the guidelines spelled out here. Policymakers should not risk the lives of U.S. troops to protect others’ interests as though those interests were our own.

Clear National Consensus

The American people must understand why they are being asked to risk blood and treasure and, crucially, they must have a say in whether to do so. The U.S. military should not be engaged in combat operations overseas unless there is a clear national consensus behind the mission.

Although modern technology allows constituents to communicate their policy preferences easily, traditional methods are just as effective in ascertaining whether the American people support the use of force. We should rely on the tool written into the Constitution: the stipulation that Congress alone, not the president, possesses the power to take the country to war.

As Gene Healy notes in this series, Congress has regularly evaded its obligations. Although the U.S. military has been in a continuous state of war over the past 15 years, few in Congress have ever weighed in publicly on the wisdom or folly of any particular foreign conflict. Some now interpret Article 5 of the North Atlantic Treaty or United Nations Security Council resolutions as obligating the United States to wage war without explicit authorization from Congress. This is unacceptable. The president may repel attacks against the United States, but the authority to deploy U.S. forces abroad, and to engage in preemptive or preventative wars of choice, resides with Congress — and by extension the people — of the United States.

Understanding of the Costs—and How to Pay Them

We must also understand the costs of war and know how we will pay them before we choose to go down that path. We cannot accurately gauge popular support for a given military intervention overseas if the case for war is built on unrealistic expectations and best-case scenarios. There is no such thing as a free lunch, and there is certainly no such thing as a free war.

Deficit spending allows the federal government to pretend otherwise. Politicians make promises, with bills coming due long after they’ve left office. But we should expect more when it comes to the use of force. Advocates for a military intervention should be forced to frame their solution in relation to costs and benefits. The debit side of the ledger includes the long-term costs of care for the veterans of the conflict. Hawks must also explain what government expenditures should be cut – or taxes increased – to pay for their war. The American people should have the final say in choosing whether additional military spending to prosecute minor, distant conflicts is worth the cost, including the opportunity costs: the crucial domestic priorities that must be forgone or future taxes paid.

Clear and Obtainable Military Objectives

We cannot compare the costs or wisdom of going to war if we do not know what our troops will be asked to do. The U.S. military should never be sent into harm’s way without a set of clear and obtainable military objectives.

Such considerations do not apply when a country’s survival is at stake. But wars of choice — the types of wars that the United States has fought in Iraq, Afghanistan, Libya, and elsewhere — are different. Advocates for such wars must demonstrate not only that the fight is necessary to secure vital U.S. interests, that it has public support, and that it has funding, but also that the military’s mission is defined and attainable.

Military victory is rarely sufficient, however, as our recent wars and interventions demonstrate. In the case of regime-change wars, ensuring that a successful transition to a stable, friendly government occurs can take a considerable amount of time and resources. Whatever replaces the defeated forces must represent a marked improvement in order for the war to advance U.S. vital interests. U.S. leaders, therefore, must not only define the military objective, but also detail what the resultant peace will look like, and how we will know the mission is complete.

It is easy for Washington to start wars, but we cannot leave U.S. troops on the hook for ending them. Policymakers must account for the tendency of war to drag on for years or more, and they must plan for an acceptable exit strategy before committing troops.

Use of Force as a Last Resort

The four criteria above are not enough to establish a war’s legitimacy, or the wisdom of waging it. After all, modern nation-states have the ability to wreak unimaginable horror on a massive scale. That obviously doesn’t imply that they should. Thus, the fifth and final rule concerning military intervention is force should be used only as a last resort, after we have exhausted other means for resolving a foreign policy challenge that threatens vital U.S. national security interests.

This point is informed by centuries-old concepts of justice. Civilized societies abhor war, even those waged for the right reasons while adhering to widely respected norms, such as proportionality and reasonable protections for noncombatants. War, given its uncertainty and destructiveness, should never be entered into lightly or for trivial reasons.

America has an exceptional capacity for waging war. U.S. policymakers therefore have a particular obligation to remember that war is a last resort. Precisely because no one else is likely to constrain them, they must constrain themselves.


U.S. foreign policy should contain a built-in presumption against the use of force. That does not mean that war is never the answer, but rather that it is rarely the best answer. Americans today enjoy a measure of safety that our ancestors would envy and that our contemporaries do envy. We generally do not need to wage war to keep it that way. On the contrary, some recent wars have degraded the U.S. military and undermined our security. Policymakers should therefore be extremely reluctant to risk American lives abroad.

The U.S. military is the finest fighting force in the world; it comprises dedicated professionals who are willing and able to fight almost anywhere, practically on a moment’s notice. Any military large enough to defend our vital national security interests will always be capable of intervening in distant disputes. But that does not mean that it should. Policymakers have an obligation to carefully weigh the most momentous decision that they are ever asked to make. These criteria can help.


Christopher Preble is vice president for defense and foreign policy studies at the Cato Institute and co-editor, with Emma Ashford and Travis Evans, of Our Foreign Policy Choices: Rethinking America’s Global Role, from which this essay is adapted.

Image: Dept. of Defense

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8 thoughts on “New Rules for U.S. Military Intervention

  1. A completely on point perceptive article. The US military is not something that should be sent willy-nilly into war like Bush2 did. Obama showed the needed caution in Ukraine over the last few years. The US has no national interests in the Ukraine. Therefore it was best left alone. That was the stance of NATO also. If the US invades any sizable country the collateral damage will kill hundreds of thousands. The US does not drop a few hundred bombs. We drop many tens of thousands.

  2. This is a good article, but it does not turn new ground; it does not reveal new criteria….Eureka concept…that should guide the national command authority in its consideration of use of force. At best, these criteria are nothing more than a slight modification of formerly espoused criteria. And what value are these or other criteria if the old adage: The first casualty of war is the truth, continues to apply? There is no value so long as politicians and their supporting mainstream media are willing to subvert the truth in order to gain public acceptance and even support for the use of military force. And there is no value in these criteria until we, the public, pay attention to ongoing events and demand better explanations as to why military force is necessary. I am a retired US Marine who served in Vietnam, the first Gulf War, and Somalia. Experience and observation have taught me that the wars/military actions in which we have engaged, at least in my lifetime, have not been for the reasons cited by our national leadership.

  3. This post is deeply flawed and does not constitute a good guide for decision-makers. Let’s walk through them one by one.

    First, it is not always clear ahead of time what is vital or not. In 1950 Acheson gave a talk in San Francisco about the location of the US security perimeter, and he excluded South Korea. This was not an omission, it was the result of a multi-agency review of the importance of South Korea to US national interest that concluded it was not vital. But that conclusion was based on geography, resources, etc. Once North Korea invaded, SK was not just SK, but an instance of communist aggression, which was in the national interest to check.

    Deterring Nazi or Imperial Japanese aggression in the late 1930’s was surely, in hindsight, a vital national interest, but most at the time did not see it so. I have seen no evidence in the decades I have spent studying international politics, that governments are a priori consistently able to ascertain what is a vital interest or not.

    Second, vital is just one gradation of national interest. Interests exist at lower levels and occasionally the warrant minimal uses of force. During the 1989 Philippine cup attempt, the US scrambled a couple of fighters to buzz the coup plotter barracks which ended up playing a role in the coup collapsing. Was the Philippines a vital national interest that warranted and invasion and occupation…no. But was it of sufficient interest to warrant coercive military signaling, yes. I could give many more examples at varying levels of intensity where small interventions in mid-range interests were a critically important to a successful policy.

    Public opinion is a wildly erratic base for foreign policy. Isolationism (toward Europe) in the 1930’s was wildly popular but really stupid. Polls about toppling the Grenadian government in 1983 were clearly against before the invasion but in favor afterward. That one turned out pretty well. Popular support for the Iraq War was very large in 2003. This is of course, why the author invokes Congressional approval.

    But we also know the fickleness of Congress is significant. It came close to not approving of the 1991 Gulf War but did approve of the 2003 Iraq War. I cannot imagine that Preble believes that 2003 was a better outcome than 1991.

    Preble is also out of line with the vast majority of practice. The US has used military force abroad over 200 times since 1789. In that 200+ years of history, there were 5 declared wars and 6 with AUMFs. So less than 5% of all interventions. He also ignores the scholarly debate on the issue of the differences between the power to DECLARE war (an archaic practice that no country does any more) and the ability to order and command the use of force. The legislative-executive balance in the constitution is not nearly as clear as he pretends.

    Understanding the cost of a war beforehand is an enormously difficult if not impossible task. It requires knowing how well your forces will fare against the enemy, how they may adapt, how we would adapt to heir adaptation, and what equipment, training etc. will be necessary to execute the adaptions to adaption that enemies make.

    Ok at the beginning, but suffers from the same problem as the last criteria. He enemy has a vote and is smart and adaptive. Military goals must shift with the conditions. Political goals may be ascertained ahead of time but military goals at the operational and tactical level must be fluid.

    This is the most pernicious of the list. A last resort criteria merely allows a problem to metastasize into a massive problem before action. Would the world have been better off with a military confrontation in the remilitarization of the Rhine rather than waiting for diplomacy to fail? We waited for a last resort in Syria and now are faced with a conflict the reenergized radical Islamists, created the worst refugee crisis since WWII, and whose effects are now partially responsible for the crisis in European integration. A wise and judicious use of force prior to a problem taking n massive scope could save lives, treasure, and stability. Of course wisdom and judgment are fickle as well.

    These criteria are notoriously difficult to apply, not subject to the level of knowledge necessary a priori, are not in line with longstanding practice and wisdom gained from past conflict.
    Checklists are never a substitute for political wisdom. Following this list would have prevented some bad interventions, but has caused other bad situations to turn horrific. I understand that people yearn for the simplicity and comfort of simple set of rules in this most consequential of endeavors, but no evidence exists that shows these rules provide better outcomes.

  4. Good article Chris. There is another dimension to this – your coalition partners. Often we follow you in – for national interests in maintaining our alliances – but often on the faith that the fight is understood and winnable. And sometimes, when things become challenging, the US balances out its need for boots on the ground by ‘strong-arming’ others to contribute. I am proud that the US and Australia have often fought for the same interests and causes but, like, you we sometimes ask searching questions about the cost to our nation’s finest.

  5. I can’t emphasize enough the criteria with respect to clear and obtainable military objectives. Additionally, I would posit that some of the political objectives (assuming that the objectives we have defined, i.e. encourage or create a more stable government in country X friendly to our interests, are in fact in our national interest) are not as easily obtained through military force as we would like to believe. As the author noted,

    “Military victory is rarely sufficient, however, as our recent wars and interventions demonstrate. In the case of regime-change wars, ensuring that a successful transition to a stable, friendly government occurs can take a considerable amount of time and resources. Whatever replaces the defeated forces must represent a marked improvement in order for the war to advance U.S. vital interests. U.S. leaders, therefore, must not only define the military objective, but also detail what the resultant peace will look like, and how we will know the mission is complete.

    It is easy for Washington to start wars, but we cannot leave U.S. troops on the hook for ending them. Policymakers must account for the tendency of war to drag on for years or more, and they must plan for an acceptable exit strategy before committing troops.”

    Starting wars is easy; ending them is harder; ending them in a way that what is left over isn’t the kind of vacuum that allows the growth of groups like ISIS is yet more difficult. Ensuring stable regime change does sound like an exceedingly broad and ill-defined concept to fit comfortably under the heading of “military objective”. And yet, that is what we have been trying to do.

    We also tend to sacrifice long-term objectives for the sake of short-term achievements, for example when we declare victory prematurely just to get boots off of the ground, forcing through an election and calling the place a democracy when there are no institutions and no incentives for the locals to create any. All we have done is bought ourselves a second go, and at a steeper price.

  6. As a non-US citizen, but a friend of the US, and a descendant of combatants on both sides of the conflicts in 1776 and 1812, this article concerns me, it is simplistic and “morally flexible”.
    In the event that Russia should intervene in the Baltic Republics, Both Britain and the US have little option but to withdraw promptly. Their is neither the required airspace nor the terms of engagement to mount a credible response to a Russian first move, under present circumstances.
    I am reluctant to elaborate on how such an intrusion might be implemented, but having looked at the options, I’d rather be playing for United than City. For those wise enough not to follow Premier League soccer, Manchester has two top football clubs, one wears blue, the other red.