Special Correspondence

Does the Cure Address the Problem? Examining the Trump Administration’s Executive Order on Immigration from Muslim-majority Countries Using Publicly Available Data on Terrorism[1]

by Daniel Milton


This Research Note offers an empirical examination of the threat from terrorism abroad in the context of the Trump Administration’s executive order restricting entry into the United States from certain Muslim countries. More specifically, it compares the number of foreign fighters coming from and the number of terrorist attacks in the countries listed in the executive order to the next highest producers of fighters and locations for terrorist attacks. The result is that, while some of the countries listed in the order have shown that they produce foreign fighters and experience terrorist activity, they are certainly not the only or most egregious targets under this standard.

Keywords: Trump, Terrorism, Travel Restrictions, Foreign Fighters, United States, Muslim countries


On January 27th, 2017, just seven days after being sworn in as the 45th President of the United States, President Donald Trump signed an executive order titled “Protecting the Nation from Foreign Terrorist Entry into the United States.” Among other effects, this executive order limited the ability of individuals from seven different countries to travel to the United States. After both public criticism and judicial proceedings, the executive order was revised and issued anew on March 6, 2017, this time with only six countries named. Following additional legal challenges, the order has remained frozen in judicial proceedings, with part of the order allowed to proceed while the U.S. Supreme Court decides the issue.

Despite the controversy surrounding the Trump Administration’s executive order, there has not been an attempt to use data on terrorist activity to examine whether or not the underlying rationale for limiting travel for the seven countries on the Administration’s list holds up to empirical scrutiny. Is there empirical evidence supporting the inclusion of Iraq, Syria, Sudan, Iran, Somalia, Libya, and Yemen on a list of countries from which terrorists are likely to come?[2] And, perhaps most contentiously, does the evidence support including those countries while excluding others? This Research Note attempts to examine those questions.

One reason such an evaluation has not been conducted previously in the open-source literature is the lack of available data that specifically focuses on issues of terrorist travel and credible plots against the U.S. homeland. Another is the simple fact that it is difficult to predict terrorist activity. While this Research Note cannot remedy the problem of prediction, it does analyze data in an effort to examine the threat emanating from abroad as it relates to the Administration’s recent executive order. It does this by comparing two sources of publicly available data on terrorist operatives and terrorist activity in the seven countries originally listed in the Administration’s executive order with countries that were not listed in the order.

This text proceeds as follows. It first briefly examines both sides of the debate on the issue of the Administration’s executive order. The article then turns to the analysis, which starts with a discussion of the strengths and limitations of the data and then examines the data on foreign fighters and terrorist attacks. It finds that, while some of the countries on the Administration’s list have produced foreign fighters and suffer from terrorist violence, others do not. In addition, some countries that experience large outflows of foreign fighters and terrorist attacks are not on the Administration’s list. In short, the examination of publicly available data provides only mixed support for the executive order. This Research Note then concludes with brief comments about protecting the U.S. homeland from the threat of terrorist attacks.

The Travel Restrictions Debate

As is the case with most complicated issues, there are various rationales on each side of the debate in relation to the travel-related restrictions imposed by the executive order.[3] Three particular arguments help set the stage for the analytic approach taken in this Research Note.

The first is that curtailing entry into the U.S. by individuals from Iraq, Syria, Sudan, Iran, Somalia, Libya, and Yemen is necessary to protect the U.S. from terrorists and terrorist groups that would come to the U.S. from abroad and do us harm. This argument assumes that the mere presence of terrorist groups and operatives in these locations makes them potentially threatening to the U.S. specifically and to the global community more broadly. Note that, under this rationale, it is the underlying instability and presence of terrorist groups in these countries that forms the rationale for preventing travel by individuals from these countries.

The second is that the order omits countries whose nationals have historically played a role in perpetrating terrorist attacks against the U.S. This point tends to revolve around the most emotionally charged and tragic terrorist event in American history: the September 11th 2001 attacks. In making this point, some reference the fact that none of the 9/11 hijackers came from the aforementioned countries, implying that the executive order is flawed. In countering this argument, one Administration official noted in an interview with CNN that the world has changed since 9/11 and that the executive order was meant to deal with current threats, not what happened in 2001.[4] The fact that the 9/11 hijackers came from particular countries, the counter-argument goes, is not sufficient evidence to target those countries in the here and now. The issue is whether or not the executive order appropriately strikes the balance between the past and the present when it comes to evaluating the threat posed by terrorist actors today. More recent data that expands beyond one incident may be useful in helping achieve this purpose.

The third argument is that outward facing travel restrictions ignore the homegrown aspect of the terrorist threat. Several reports and studies have pointed to a recent increase in such incidents on the part of a wide variety of groups, from violent jihadists to violent racists.[5] However, some research has also suggested that the domestic threat, particularly that which stems from Muslim Americans, is not as likely as some may posit.[6]

Although the homegrown argument is important to evaluate, there are two reasons it is not discussed in detail here. First, there is a more robust amount of discussion and research on this topic. Based on this research, it seems clear that, although there is debate about the size of the homegrown terrorist threat, the threat is something that exists and should be a focus for the intelligence community and law enforcement professionals. Second, the existence of a homegrown threat does not mean there is no external threat. However, comparatively less discussion has been devoted to evaluating the foreign threat rationale outlined in support of the travel restrictions. This Research Note remedies that and examines publicly available, empirical evidence to help evaluate the claim that the countries on the Administration’s list pose the greatest foreign terrorist danger to the U.S.

Using Publicly Available Data to Assess the Terrorist Threat to the United States

Although the ideal data to evaluate the rationale underlying the Administration’s executive order is not publicly available, there are some data sources that can offer insight into this question. The use of publicly available data is not without its limitations. For example, the data often has a certain time lag, meaning it is a bit dated by the time it is used for analysis. Additionally, academics have noted the many challenges of collecting terrorism data from news reporting.[7] Another limitation of the data used here is that it is based on attacks and fighter profiles, but it obviously cannot tell us specifically from whom and where attacks will actually come.[8] Terrorism, after all, is a dynamic phenomenon.

In short, while not identifying with exactness the most prominent threat of terrorism faced in real time, publicly available data does provide the opportunity for a more informed discussion about whether limiting the entry of individuals from the seven countries is consistent with the threat as illustrated by recent experience with terrorism. Using this data is not a substitute for more recent or detailed intelligence reporting, but can serve to stimulate public debate by providing a greater level of clarity on where threats may come from and what some challenges are in trying to deal with those threats.

Given the focus in the Administration’s executive order regarding Syria, the ongoing Syrian civil war seems like a good place to begin an assessment of the threat posed by terrorists to the U.S. When it comes to threats emanating from Syria that have the potential to impact the U.S. homeland, one prominent topic of concern is that of foreign fighters.

According to the U.S. State Department, more than 40,000 individuals from over 120 countries have come to Syria to fight for one of the many opposition groups.[9] Part of the Administration’s concern about Syria is the fact that many individuals have gone there to fight with groups that view the U.S. as an enemy. Those who make it to groups such as the Islamic State likely receive a religious indoctrination in the group’s worldview, as well as practical experience using weapons and fighting.

Looking at detailed information on foreign fighters could provide an interesting assessment of at least two components of the terrorist threat. The most obvious is that such data could speak to the scope of the threat posed by the eventual return of these foreign fighters. One of the most prominent concerns is that returning fighters, having been further radicalized and trained by groups like the Islamic State, will be able carry out more effective attacks in their homelands or in other countries to which they may travel.[10]

The second issue to which this data speaks is a bit more obscure, but equally important. The data, by identifying which countries have challenges with radicalized individuals leaving to become foreign fighters, also provides a proxy for understanding where the Islamic State’s narrative appears to have gained significant traction. Countries with a large foreign fighter problem are more likely to have a domestic radicalization problem. When it comes to the threat posed to the U.S., it will ultimately matter little to the public if the terrorist carrying out the attack came from Iraq and Syria or was radicalized in Germany and came directly to the United States.[11]

The Combating Terrorism Center at West Point conducted an analysis of the foreign fighter threat using data from the Islamic State’s own foreign fighter entry forms. This data, which was obtained from NBC News, gives an inside look into the organization’s recruitment profile, and, by extension, where the threat comes from. To help answer the question at hand, I took the CTC’s public report and identified what percentage of the foreign fighters came from the seven countries identified in the executive order. This information appears in Table 1.

It should be noted that Iraq and Syria are not represented in Table 1 because the data likely did not contain a representative amount of fighters from those countries. This is due to the fact that the data focused mainly on foreign fighters, whereas most Iraqis and Syrians would be considered local fighters.

Given that caveat, a couple of interesting findings emerge. First, the countries listed in the executive order contribute a relatively small number of overall number of fighters. More precisely, the five countries for which we have data contribute about 4% of the foreign fighters. Second, of those five countries, only Libya seems to provide a substantial number when their population is taken into consideration. This should not come as a surprise, given that Libya was also a key provider of fighters to the Iraqi insurgency that peaked in 2006 - 2007.[12]



For comparison, the same procedure was repeated for the top seven producers of foreign fighters in the CTC report (in terms of the absolute number of records), provided they were not on the Administration’s list of countries. It is interesting to note that, in terms of the absolute number of fighters, not a single one of the five countries listed by the Administration is in the top seven foreign fighter producing countries, which are shown in Table 2.



These seven countries account for 63% of the records in the CTC dataset. That represents a far greater amount of foreign fighters than do the countries on the Administration list. Even if one limited the comparison five countries, such a procedure still captures 27% of all fighters at the lower end (if the calculation uses the bottom five countries in Table 2) and 54% on the high end (if the top five countries are included). In short, if the worry is that those who have traveled to fight on behalf of the Islamic State may eventually return or otherwise threaten the U.S., the five countries listed in the executive order would not seem to be of highest priority based on these numbers.

While each of these countries and their respective security challenges when it comes to terrorism deserves a much more in depth treatment than can be undertaken in this Research Note, just a few brief observations are offered here. Saudi Arabia tops the list. Taken together with the fact that 15 of the 19 hijackers on 9/11 came from Saudi Arabia in 2001, the sizable number of foreign fighters leaving the country and going to fight in Syria speaks to the continuing radicalization challenge faced by the Saudi Arabian government and to their difficulty in preventing travel. Tunisia, which experienced the highest per capita outflow of foreign fighters in the database, has been challenged by political and economic issues at home. Turkey, an aspirant to the Visa Waiver Program, stands out as a uniquely challenging case. It has been an at times frustrating partner in the fight against the Islamic State, even as it continues to arrest large numbers of “radicals” within its borders.[13] Russia and China’s place on the list is primarily due to the flow of individuals from their respective restive regions that are home to violent jihadist groups (Chechnya and Xinjiang).

Also worth mentioning and potentially of equal concern, but not present in Table 2, is the sizable number of foreign fighters who have traveled from Europe to join the Islamic State. If we take the top five European countries in the CTC dataset (France, Germany, United Kingdom, Belgium, Denmark), the total number of foreign fighters is 304, or about 7.6% of the total dataset. This is a greater proportion than that obtained by grouping together the five countries covered by the executive order. This raises the question about whether the attempt to limit travel from certain countries actually makes the country that much safer, given that the threat appears to be spread among a wider range of countries. Indeed, some of the countries that have produced large numbers of foreign fighters receive no scrutiny in the executive order.

Of course, this is just data related to foreign fighters. What can be said about the problem of terrorism more holistically? An assessment of which countries are currently the “hot zones” as far as terrorism goes may be more in line with the seven countries with which the Administration has expressed the most concern. Fortunately, data on terrorist activity around the world is available through the Global Terrorism Database (GTD), which is maintained by the University of Maryland’s National Consortium for the Study of Terrorism and Responses to Terrorism (START). Using this dataset, data was collated on terrorist activity in every country around the world for the two most recent years in the database (2014-2015). The data for the countries listed in the Administration’s executive order can be seen in Table 3.



The second column shows the number of attacks that occurred in each country from 2014 to 2015. The third column shows the proportion of a country’s attacks as a percentage of all terrorist attacks worldwide in the GTD during that two year span. The results of this simple comparison are telling. Iraq pops as being the location in which 21 percent of all terrorist attacks around the world took place, the largest single number for any other country.[14] After accounting for Iraq, however, the percentage covered by the remaining six countries listed in the Administration’s executive order drops quite a bit. In absolute numbers, however, there is no denying that just about every single one of these countries has some form of a terrorism problem. This may lead some to conclude that preventing travel from these countries in which terrorism occurs so frequently makes good policy sense.

An important caveat needs to be made here. It is entirely probable that the number of terrorist attacks that occurred in 2016 in these countries is even higher than it was for the 2014 - 2015 time period. Each of these countries, with the exception of Iran, remains locked in intense internal armed conflict.

But what of the rest of the countries that were not included in the executive order? Table 4 lists the next seven largest countries in terms of the number of attacks that took place in their borders, as well as how much each country’s number of attacks represents as a proportion of the number of all terrorist attacks in the GTD database.



A look at the countries in Table 4 certainly raises questions. Afghanistan and Pakistan, where the United States continues to conduct counterterrorism strikes to limit the ability of al-Qa’ida to carry out attacks around the world and to protect the U.S. troops stationed in theater, are places of prominent concern. The 2010 Times Square bombing attempt had its roots in Pakistan. Nigeria is home to one of the most violent terrorist groups in the world, Boko Haram.[15] Egypt is the home to a very potent affiliate of the Islamic State, known as the Islamic State - Sinai. This group has reportedly carried out attacks against U.N. peacekeeping forces and claimed responsibility for downing an airliner.[16] Finally, the Philippines has recently been the scene for dramatic developments, particular in the southern city of Marawi.[17] In short, there seem to be plenty of areas of concern beyond the countries listed in the executive order when it comes to potential terrorist threats facing the homeland.


This Research Note utilized publicly available data in an effort to evaluate part of the rationale underlying the Trump Administration’s executive order limiting travel by individuals from certain countries into the U.S. The simple data analysis used here provided only mixed support for the Administration’s executive order. Some of the countries in the Administration’s list of travel restrictions indeed have a terrorist problem. In others, the threat posed by terrorism is less clear. The same is true for countries not on the list; some have severe terrorism challenges, others do not.

To be clear, the argument here is not that travel restrictions need to be implemented in relation to a wider array of countries. Nor is it that such policies are failed from the start. Instead, the main takeaway from this examination of publicly available data is that if policymakers mistake the seven countries listed in the Administration’s order as the sole or primary source of our terrorism problems, then the risk of being blindsided by terrorist threats coming from other locations and through other avenues is increased. Beyond that point, simply restricting or cutting off travel completely (particularly once the broader nature of the threat is correctly diagnosed) is not likely the most feasible or effective solution, practically or politically. Limiting the threat posed by terrorists from abroad will require an array of policy solutions that address each stage of the process whereby an individual radicalizes, trains, travels, obtains materials, and ultimately carries out an attack against the U.S.

Of course, many of these solutions focus on the possibility of terrorism coming from the outside into the U.S. As noted earlier, however, the terrorism threat the U.S. faces has a significant domestic manifestation that is not limited to a particular ideology. While assessing the domestic threat of terrorism is beyond the scope of this Research Note, addressing it will almost certainly require different counterterrorism tools than those applied to prevent the transnational component. To make matters even more complicated, often the domestic and transnational components intersect, creating additional challenges for U.S. counterterrorism efforts that may not work seamlessly across these gaps.

In short, while it may be appealing to think that the threat is limited by geography, combating terrorism is challenging precisely because terrorism simply cannot be contained through one policy instrument or dealing with a small number of countries. Designing policies that effectively combine multiple facets of the U.S. government’s counterterrorism capabilities towards this global threat is the key to achieving the desired measure of security.

N.B.: The views expressed in this article are those of the author and not of the U.S. Military Academy, the Department of the Army, or any other agency of the U.S. Government.

About the Author: Daniel J. Milton earned his Ph.D. in Political Science from Florida State University. He is the author or co-author of several recent monographs on the Islamic State’s propaganda efforts, the foreign fighter threat, and the hostage taking of Westerners by jihadist groups. His work has appeared in various national and international media outlets. He is currently the Director of Research at the Combating Terrorism Center at the United States Military Academy. He is also an Assistant Professor in the Department of Social Sciences at the United States Military Academy. Prior to West Point, he taught at Arkansas State University and Brigham Young University.


[1] The author would like to thank Brian Dodwell, Bryan Price, and Dakota Foster for their comments and critiques on earlier versions of this note. It is much improved because of their feedback.

[2] Iraq was removed in the Administration’s revision of the original executive order. However, for purposes of this article, it was considered together with the remaining six countries in the executive order.

[3] For a look at the legal debate of the order’s constitutionality, see Rivkin, D.B., Tumlin, K., & Downie, J. (2017). “Is President Trump’s Executive Order Constitutional?” Washington Post, 6 February. URL: For an overview of other impacts of the order, see Calamur, K. (2017). “What Trump’s Executive Order on Immigration Does – and Doesn’t Do.” Atlantic, 30 January. URL:

[4]For one example of a debate over the 9/11 hijackers and the Administration’s rebuttal on this point, see

[5] Perliger, A. (2013). Challengers from the Sidelines: Understanding America’s Violent Far-Right. West Point, NY: Combating Terrorism Center; Crone, M. & Harrow, M. (2011). “Homegrown Terrorism in the West.” Terrorism and Political Violence 23(4), 521 - 536.

[6] Bergen, P. (2017). “Trump’s Travel Ban is Useless. Terrorists Mostly Come from Our Own Backyard.” Washington Post, June 5, 2017. URL:; Mueller, J. & Stewart, M.G. (2012). “The Terrorism Delusion: America’s Overwrought Response to September 11.” International Security 37(1), 81 - 110; Brooks, R.A. (2011). “Muslim ‘Homegrown’ Terrorism in the United States: How Series is the Threat?” International Security 36(2), 7 - 47.

[7] Drakos, K. & Gofas, A. (2006). “The Devil You Know but Are Afraid to Face: Underreporting Bias and its Distorting Effects on the Study of Terrorism.” Journal of Conflict Resolution 50(5), 714 - 735.

[8] To be fair, classified data cannot tell us which individuals are likely to pose a threat either. This has more to do with the fact that terrorism has proven to be an attractive tactic for a wide range of individuals across different demographic groups, nationalities, and ideologies. In other words, research to this point has not found the profile of a terrorist, if it exists. Horgan, J. (2003). The Psychology of Terrorism. London: Taylor and Francis.

[9] The number of fighters and the diverse nature of their origins is staggering. These numbers come from a 2016 State Department press conference, which is available at URL:

[10] That foreign fighters pose a threat is clear. What is less clear is how much of a threat they pose and whether or not that threat is changing over time. See: Byman, D. and Shapiro, J. (2014). Be Afraid, Be A Little Afraid: The Threat of Terrorism from Western Foreign Fighters in Syria and Iraqi. Washington, DC: Brookings Institution.; Byman, D. (2015). “What Do The Paris Attacks Tell Us About Foreign Fighters?” Washington Post, 16 November. URL:

[11] That said, from a practical standpoint, research has suggested that returnees are more effective at carrying out operations than those who are not veterans of foreign campaigns. Hegghammer, T. (2013). “Should I Start or Should I Go? Explaining Variation in Western Jihadists’ Choice between Domestic and Foreign Fighting.” American Political Science Review 107(1), 1 - 15.

[12] A recent report from the CTC compared the flow of foreign fighters during 2006-2007 timeframe to the flow that came more recently into Syria to support the Islamic State. Dodwell, B., Milton, D., & Rassler, D. (2016). Then and Now: Comparing the Flow of Foreign Fighters to AQI and the Islamic State. West Point, NY: Combating Terrorism Center. URL:

[13] Kingsley, P. (2017). Turkey Arrests Hundreds in Sweeping Raids Against ISIS.” New York Times, 5 February. URL:; No Author. (2016). “Istanbul Attacks: Turkish Police Arrest 235 of ‘militant links.’” BBC, 12 December. URL: Moore, J. (2016). “Turkey’s President Erdogan Accuses U.S. Coalition of Supporting ISIS.” Newsweek, 28 December. URL:

[14] And, as it turns out, Iraq was removed from the Administration’s revised order.

[15] Deman, E. (2015). “The World’s Deadliest Terrorist Organization: It’s Not ISIS.” Atlantic, 18 November. URL:

[16] Tilghman, A. (2015). “IEDs Injure U.S. Troops Deployed on New ISIS Front in Egypt.” Military Times, 4 September. URL:; Starr, B. and Shoichet, C.E. (2015). “Russian Plane Crash: U.S. Intel Suggests ISIS Bomb Brought Down Jet.” CNN, 4 November. URL:

[17] Paddock, R. and Villamor, F. (2017). “Destroying a Philippine City to Save It From ISIS Allies.” New York Times, 13 June. URL:

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Perspectives on Terrorism is  a journal of the Terrorism Research Initiative and the Center for Terrorism and Security Studies

ISSN  2334-3745 (Online)

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