US military intervention abroad

Lane Kenworthy, The Good Society
June 2019

For the past century, since its entry into the first world war in 1917, the United States has periodically intervened militarily in other nations. When should America intervene? When is its intervention likely to do good?

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Because there is no democratically-elected supranational government to police the world, the default principle guiding thinking about military intervention has been national sovereignty, or self-determination. Countries should not interfere in the affairs of other countries. This was formalized in a resolution adopted by the United Nations General Assembly in 1965, according to which “No State has the right to intervene, directly or indirectly, for any reason whatever, in the internal or external affairs of any State. Consequently, armed intervention and all other forms of interference or attempted threats against the personality of the State or against its political, economic, and cultural elements are condemned…. No state shall organize, assist, foment, finance, incite, or tolerate subversive, terrorist, or armed activities directed toward the violent overthrow of another state, or interfere in civil strife in another state.”1

At the same time, few have believed that this principle should be absolute. For much of the past two centuries, the most common justifications for intervention were

  • National interest of the intervening country
  • Preemptive self-defense

From 1945 to 1989, cold war considerations dominated US decisions about intervention, covert operations, and foreign aid.2 The justification was a combination of national interest and preemptive self-defense. The guiding question in deciding whether and where to intervene was: What will be the impact on the Soviet Union’s strength and reach, and therefore on its ability to harm us? The chief exception was Jimmy Carter’s attempt, during his presidency in the late 1970s, to make human rights a key consideration.

With the end of the cold war in 1989-91, the United States and other rich countries began to consider different motivations for intervention:

  • Humanitarian
  • Democracy

The humanitarian motive refers to intervention aimed at stopping or reversing a humanitarian crisis such as massacres of civilians, forced displacement of populations, large-scale sexual violence, or some other significant violation of human rights.3 Examples before and during the cold war include the Turkish killing of Armenians 1915, the USSR under Stalin 1917-54, Chinese nationalists 1927-49, Nazi Germany 1933-45, China’s “Great Leap Forward” and “Cultural Revolution” 1950s-60s, Indonesia 1965, the Burundi massacre of Hutus 1972, Cambodia’s Pol Pot regime 1975-78, Uganda’s Idi Amin regime 1972-79, and Guatemala’s massacre of Mayans 1981-83. Post-cold-war examples include the Rwanda slaughter of Tutsis 1994, the Congo war 1996ff, the Serb massacre of Bosnians 1995, Darfur 2003ff, Syria 2011ff. However, in most of these cases, the United States did not intervene.

The democracy motive has two variants. The first aims to reverse the overthrow of a democratic government.4 The second is proactive installation of democracy.5 The latter was George W. Bush’s post-hoc rationale for the 2003 invasion of Iraq (the original justification was preemptive self-defense). It’s more controversial than addressing a humanitarian crisis or reversing the overthrow of a democratic government.


Some believe there is little or no chance American military intervention can do good. In the words of one commentator, “The consequences of US troop wars, air wars, drone strikes, and special ops include brutality and suffering faced by local people. They also involve the empowerment of reactionary forces in those regions as well as the destabilization of civil and democratic spaces…. Being against destructive, US-led state violence around the world should be a given.”6

For those who are more optimistic, the decision about when and where to intervene ought to take into account five considerations7:

1. How serious is the harm? Stalin’s regime in the former USSR is estimated to have caused the death of more than 60 million people. The number of Bosnian civilians killed by Serbs in the early 1990s is thought to have been about 50,000. In the Syrian crisis, approximately 400,000 people have been killed and an estimated 13 million, more than half of the country’s population, have been displaced.8

Those are instances in which intervention clearly seems justified. Other cases are more difficult. For instance, what about a military leader who overthrows a democratically-elected but inept or corrupt president and promises elections relatively soon (Egypt 2013)?

2. Can intervention solve the immediate problem? Can the bad guys be defeated? Might intervention result in increased death, injury, or displacement of the good guys?9 US successes in Grenada 1983, Kuwait 1991, and Bosnia 1995 suggested grounds for optimism. But the interventions in Iraq 2003-11 and Afghanistan 2001-14 were much less successful in this respect.

3. Is the medium- and long-run impact likely to be positive? There are a number of potential problems: reconstruction difficulties, severe economic disruption, a shortage of capable and honest political leaders, destruction of civil society, and the impact on neighboring countries and the region. For instance, America’s invasion of Iraq may have enhanced Iran’s influence in the region. On the other hand, it was hoped that if Iraq could form a stable democracy it would increase pressure for democracy in nearby countries (“Arab spring”).

There is inevitably a degree of uncertainty about what the medium- or long-run consequences will be. Societies are complex systems. It’s very difficult to predict based on past experience, because each case is unique.10

4. Is the likely cost to Americans bearable? Here are the number of dead and wounded US soldiers from some past US military interventions:11

  • World War I 1917-18: 117,000 dead, 204,000 wounded
  • World War II 1941-45: 405,000 dead, 671,000 wounded
  • Korea 1950-53: 37,000 dead, 103,000 wounded
  • Vietnam 1964-73: 58,000 dead, 153,000 wounded
  • Kuwait 1991: 400 dead, 500 wounded
  • Bosnia and Kosovo, 1995 and 1999: 32 dead, 8 wounded
  • Afghanistan 2001-14: 2,300 dead, 20,000 wounded
  • Iraq 2003-11: 4,500 dead, 32,000 wounded
  • Libya 2011: 0 dead, 2 wounded

There is also financial cost. The United States spends 4-5% of its GDP each year on the military.12 Here is the monetary cost of interventions, expressed as share of GDP during the war’s peak year:

  • World War I: 14% of GDP
  • World War II: 36%
  • Korea: 4%
  • Vietnam: 2%
  • Kuwait: ?
  • Bosnia and Kosovo: ?
  • Afghanistan: 0.8%
  • Iraq: 1%
  • Libya: 0.01%

Because of the human and financial cost of a military intervention, domestic political support can erode if success doesn’t come quickly and smoothly. Television, the internet, and social media have greatly increased citizens’ access to information about the nature and progress of wars. A lengthy humanitarian intervention is harder to justify domestically than one based on national interest. It helps to spread the personnel and financial burden across a coalition of countries.

In Syria, the US government has supplied weapons to groups attempting to overthrow the regime of Syrian President Assad, and it has launched air attacks against the group that calls itself ISIS or ISIL. But the Obama administration was not willing to send American ground troops. Several days after the terrorist attacks in Paris on November 13, 2015, President Obama was asked in a press conference whether it was time for a more aggressive approach. In his response, Obama emphasized that an effective commitment of ground troops would have to be a large and lengthy one.13

“Well, keep in mind what we have been doing. We have a military strategy that is putting enormous pressure on ISIL through airstrikes, that has put assistance and training on the ground with Iraqi forces. We’re now working with Syrian forces as well to squeeze ISIL, cut off their supply lines. We’ve been coordinating internationally to reduce their financing capabilities, the oil that they’re trying to ship outside. We are taking strikes against high-value targets…. As we find additional partners on the ground that are effective, we work with them more closely. I’ve already authorized additional Special Forces on the ground who are going to be able to improve that coordination….

“And on the diplomatic front, we’ve been consistently working to try to get all the parties together to recognize that there is a moderate opposition inside of Syria that can form the basis for a transition government, and to reach out not only to our friends but also to the Russians and the Iranians who are on the other side of this equation to explain to them that ultimately an organization like ISIL is the greatest danger to them, as well as to us.

“So there will be an intensification of the strategy that we put forward, but the strategy that we are putting forward is the strategy that ultimately is going to work. But as I said from the start, it’s going to take time.

“What’s been interesting is, in the aftermath of Paris, as I listen to those who suggest something else needs to be done, typically the things they suggest need to be done are things we are already doing. The one exception is that there have been a few who suggested that we should put large numbers of US troops on the ground.

“We have the finest military in the world and we have the finest military minds in the world, and I’ve been meeting with them intensively for years now, discussing these various options, and it is not just my view but the view of my closest military and civilian advisors that that would be a mistake — not because our military could not march into Mosul or Raqqa or Ramadi and temporarily clear out ISIL, but because we would see a repetition of what we’ve seen before, which is, if you do not have local populations that are committed to inclusive governance and who are pushing back against ideological extremes, that they resurface, unless we’re prepared to have a permanent occupation of these countries.

“And let’s assume that we were to send 50,000 troops into Syria. What happens when there’s a terrorist attack generated from Yemen? Do we then send more troops into there? Or Libya, perhaps? Or if there’s a terrorist network that’s operating anywhere else — in North Africa, or in Southeast Asia?

“So a strategy has to be one that can be sustained. And the strategy that we’re pursuing — which focuses on going after targets, limiting wherever possible the capabilities of ISIL on the ground, systematically going after their leadership, their infrastructure, strengthening Shia, or strengthening Syrian and Iraqi forces and Kurdish forces that are prepared to fight them, cutting off their borders and squeezing the space in which they can operate until ultimately we’re able to defeat them — that’s the strategy we’re going to have to pursue.”

5. Is international authorization needed? International institutions such as the United Nations and NATO are helpful, and one way to boost their legitimacy and effectiveness is for the United States to secure their approval for foreign military interventions. Indeed, Matthew Yglesias has argued that the projected impact on international institutions and rules should be the dominant consideration guiding any intervention decision.14 He suggests that this aim guided much of post-WW1 Democratic presidents’ foreign policy, from Woodrow Wilson to Bill Clinton. But there are difficult cases. In Kosovo 1999, the UN refused to authorize, so we acted through NATO. Another is Iraq 2003. Suppose the UN had authorized President Bush’s request to invade? Would it have been the right thing to do? A third is Darfur 2004. Because of China’s objection, the UN refused to authorize deployment of troops on the ground. Africa is beyond NATO’s orbit. Would it have been wrong for the US to go in alone to stop the genocide?

Prior to 1990, most American interventions weren’t authorized by a supranational body, and that also was true of Afghanistan 2001 and Iraq 2003. But a number of US interventions in recent decades have been authorized by the United Nations: Kuwait 1990, Somalia 1993, Haiti 1994, Bosnia 1995. Some others have been authorized by a regional alliance, such as NATO: Kosovo 1999, Libya 2011.

China and Russia each have a veto in the United Nations, and it can be difficult to secure their agreement. Some therefore favor forming a new “League of Democracies” to replace the UN. However, this would formally split the world into two camps, and many experts believe the best way to deal with China and other nondemocracies is to work with them rather than against them.15


We have little polling data on the specific question of humanitarian military intervention, but a number of surveys ask closely related questions. As we see in figures 1-6, Americans tend to be split on whether it’s best for the country or the world for the US to “be active in world affairs” or “mind our own business internationally,” though on most questions the majority favor an interventionist or internationalist approach. While figure 1 suggests reduced support for an active role in the 1960s and 1970s (Vietnam) and in the 2000s (Iraq), responses to other questions suggest no such change.

Figure 1. Disagree the US should mind its own business internationally
Estimated share of US adults. Question: “The U.S. should mind its own business internationally and let other countries get along the best they can on their own.” Response options: agree, disagree. The line shows the share choosing disagree, with don’t know responses excluded. Data sources: Gallup for 1964-1991; Pew Research Center for 1993ff.

Figure 2. It’s best for the future of the US if we take an active part in world affairs
Estimated share of US adults. CCGA question: “Do you think it will be best for the future of the country if we take an active part in world affairs or if we stay out of world affairs?” The line shows the share responding take an active part, with don’t know responses excluded. Data source: Chicago Council on Global Affairs, “America Engaged: American Public Opinion and US Foreign Policy,” 2018. Pew qestion: “Which statement comes closer to your views, even if neither is exactly right? (1) It’s best for the future of our country to be active in world affairs. (2) We should pay less attention to problems overseas and concentrate on problems here at home.” The line shows the share choosing response 1, with don’t know/both/neither responses excluded. Data source: Pew Research Center, “Large Majorities in Both Parties Say NATO Is Good for the U.S.,” 2019.

Figure 3. Problems in the world would be even worse without US involvement
Estimated share of US adults. Question: “Which statement comes closer to your views, even if neither is exactly right? (1) U.S. efforts to solve problems around the world usually end up making things worse. (2) Problems in the world would be even worse without U.S. involvement.” The line shows the share choosing response 2, with don’t know/both/neither responses excluded. Data source: Pew Research Center, “Large Majorities in Both Parties Say NATO Is Good for the U.S.,” 2019.

Figure 4. The US should maintain or increase our commitment to NATO
Estimated share of US adults. Question: “Do you feel we should increase our commitment to NATO, keep our commitment what it is now, decrease our commitment to NATO, or withdraw from NATO entirely?” The line shows the share responding increase or keep as is, with don’t know responses excluded. Data source: Chicago Council on Global Affairs, “America Engaged: American Public Opinion and US Foreign Policy,” 2018.

Figure 5. The US should take into account the interests of our allies even if it means making compromises with them
Estimated share of US adults. Question: “Which statement comes closer to your views, even if neither is exactly right? (1) In foreign policy, the U.S. should take into account the interests of its allies even if it means making compromises with them. (2) In foreign policy, the U.S. should follow its own national interests even when its allies strongly disagree.” The line shows the share choosing response 1, with don’t know/both/neither responses excluded. Data source: Pew Research Center, “Large Majorities in Both Parties Say NATO Is Good for the U.S.,” 2019.

Figure 6. The US should be more willing to make decisions within the United Nations
Estimated share of US adults. Question: “Do you agree or disagree: When dealing with international problems, the United States should be more willing to make decisions within the United Nations even if this means that the United States will sometimes have to go along with a policy that is not its first choice.” The line shows the share saying agree, with don’t know responses excluded. Data source: Chicago Council on Global Affairs, “America Engaged: American Public Opinion and US Foreign Policy,” 2018.


There is need, precedent, moral justification, and authorization by the United Nations (as a general principle). Yet at the moment, prospects are mixed.

Begin with the need for intervention. There is plenty. Examples in recent decades include Iraq’s occupation of Kuwait in 1990, Somalia 1993, the coup in Haiti in 1994, the Rwanda genocide in 1994, the Congo civil war 1996ff, the attempted coup in Sierra Leone in 2000, the Darfur (Sudan) genocide 2003ff, the Myanmar cyclone devastation 2008, and the Syrian crisis 2011ff. There are additional less well-known situations in Africa and Asia along with assorted suppressions of democratic movements in the Middle East.

There is ample precedent for successful intervention, and it stretches over a long period of modern history. Though the question seems a new one (a product of the end of the cold war), actually there were several humanitarian interventions by Britain and France in the 1800s.16 And in the 1990s there were successful multinational UN-authorized interventions in Kuwait and Bosnia.

Along with need and precedent, there is moral justification. Many agree that intervention is morally justified in cases of humanitarian crisis.

Finally, there is support from the United Nations. In 2005 the UN’s General Assembly ratified a new approach to humanitarian intervention, commonly referred to as the responsibility to protect.17 It declares that “The international community, through the United Nations, has the responsibility … to help to protect populations.” This, for the first time in human history, formally overrides the principle of national sovereignty, though each individual intervention still requires a specific authorization by the UN.

The Obama administration — the president, Secretaries of State Hillary Clinton and John Kerry, and UN Ambassadors Susan Rice and Samantha Power — were supportive of humanitarian intervention, including in Libya in 2011. The administration was much more hesitant about Syria, but that’s not surprising, as the likelihood of success was much lower.

However, despite need, precedent, moral justification, and general UN authorization, support for humanitarian intervention among American citizens and policy makers seems to have dimmed.18 The September 11, 2001 terrorist attacks turned the focus of rich countries toward domestic security and anti-terrorism. The “weapons of mass destruction” mistake in Iraq has heightened concern about whether the quality of information we typically have is sufficient to justify intervention. The economic and political ascendance of China and Russia reduce the likelihood of UN Security Council approval of humanitarian intervention. The US action in Iraq has shifted sentiment against unilateral intervention. The results of the Iraq, Afghanistan, and Libya invasions have reduced confidence in humanitarian intervention’s potential to improve well-being. Moreover, going forward, it’s possible that Americans will come to think everything can be solved with drones instead of US soldiers.


Arguably, the world would be a better place if there were more well-done humanitarian intervention. The end of the cold war, the 1990s Kuwait and Bosnia precedents, and the UN’s 2005 “Responsibility to Protect” resolution have made this possible.

But there are big obstacles. The decision about whether to intervene hinges on a host of complex considerations. And the threat of terrorism, China and Russia’s oppositional stance at the UN, and the US experiences in Iraq, Afghanistan, and Libya have, for the moment, acted as a brake.

  1. United Nations, “Declaration on the Inadmissibility of Intervention in the Domestic Affairs of States and the Protection of Their Independence and Sovereignty,” General Assembly Resolution 2131, 1965. 
  2. Hans Morgenthau, “To Intervene or Not to Intervene?,” Foreign Affairs, 1967. 
  3. Michael Walzer, Arguing about War, Yale University Press, 2004. 
  4. Paul Collier, Wars, Guns, and Votes, Harper, 2009. 
  5. Robert Kagan and William Kristol, Present Dangers, Encounter Books, 2000. 
  6. Tejasvi Nagaraja, “On Foreign Policy: War from Above, Solidarity from Below,” in We Own the Future: Democratic Socialism — American Style, edited by Kate Aronoff, Peter Dreier, and Michael Kazin, New Press, 2020, p. 191. 
  7. Other criteria are possible. Here is Tony Blair’s version, from 1999: “Looking around the world there are many regimes that are undemocratic and engaged in barbarous acts. If we wanted to right every wrong that we see in the modern world then we would do little else than intervene in the affairs of other countries. We would not be able to cope. So how do we decide when and whether to intervene? I think we need to bear in mind five major considerations. First, are we sure of our case? War is an imperfect instrument for righting humanitarian distress, but armed force is sometimes the only means of dealing with dictators. Second, have we exhausted all diplomatic options? We should always give peace every chance…. Third, on the basis of a practical assessment of the situation, are there military operations we can sensibly and prudently undertake? Fourth, are we prepared for the long term? In past we talked too much of exit strategies. But having made a commitment we cannot simply walk away once the fight is over; better to stay with moderate numbers of troops than return for repeat performances with large numbers. And finally, do we have national interests involved? … I am not suggesting that these are absolute tests. But they are the kind of issues we need to think about in deciding in the future when and whether we will intervene.” Tony Blair, Speech to the Chicago Economic Club, April 22, 1999. 
  8. Wikipedia, “Casualties of the Syrian War”; Phillip Connor, “Most Displaced Syrians Are in the Middle East, and about a Million Are in Europe,” Pew Research Center, 2018. 
  9. William Easterly argues that military presence makes it easier for the bad guys to obstruct efforts by humanitarian aid providers. Easterly, “Foreign Aid Goes Military,” New York Review of Books, December 4, 2008. 
  10. Francis Fukuyama, “After Neoconservatism,” New York Times, 2004. 
  11. “United States Military Casualties of War,” Wikipedia. 
  12. Dinah Walker, “Trends in U.S. Military Spending,” Council on Foreign Relations, 2014. 
  13. “Press Conference by President Obama — Antalya, Turkey,” November 16, 2015. 
  14. Matthew Yglesias, Heads In the Sand, Wiley, 2008. 
  15. Fareed Zakaria, The Post-American World, W.W. Norton, 2008. 
  16. Gary J. Bass, Freedom’s Battle, Knopf, 2008. 
  17. Gareth Evans, The Responsibility to Protect, Brookings Institution Press, 2008. 
  18. Richard Just, “The Truth Will Not Set You Free,” The New Republic, 2008.