Walls and Strategic Innovation in Violent Conflict

• Author: Matthew Nanes,Trevor Bachus
• Published date: 01 July 2021
• Date: 01 July 2021
• DOI: 10.1177/0022002721994667
• Subject Matter: Articles

Article

Walls and Strategic

Innovation in

Violent Conflict

Matthew Nanes

1

and Trevor Bachus

1

Abstract

Governments build walls to curtail a range of illicit activities like immigration, crime,

and terrorism. We argue that while physical barriers effectively prevent specific

unwanted behavior, they induce actors to respond strategically and develop new

tactics, changing the nature of illicit activity and leading to new threats. We test this

argument in the context of Israel’s security barrier. Using an instrumental variable

unrelated to the underlying threat of attack, we analyze short-term changes in the

barrier’s porousness. Terror attacks in Israel are less likely when the barrier is more

secure. However, we also observe evidence of changing strategies. Attacks are most

likely immediately after the government eases temporary restrictions on movement,

suggesting that previously-planned attacks were delayed, not prevented. Further-

more, when the barrier is more secure, terrorists select weapons that are less

affected by it and carry out attacks in systematically different locations. Ultimately,

walls’ impacts on any challenge depend not just on how well they prevent movement

but also on illicit actors’ strategic responses.

Keywords

conflict management, counterterrorism, Israeli-Palestinian conflict, terrorism

Governments worldwide use walls and other physical barriers to limit undesired

movement of people and goods, including illegal immigration (Hassner and

1

Department of Political Science, Saint Louis University, St. Louis, MO, USA

Corresponding Author:

Matthew Nanes, Department of Political Science, Saint Louis University, 3750 Lindell Blvd, St. Louis, MO

63108, USA.

Email: matthew.nanes@slu.edu

Journal of Conflict Resolution

2021, Vol. 65(6) 1131-1158

ªThe Author(s) 2021

Article reuse guidelines:

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DOI: 10.1177/0022002721994667

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Wittenberg 2015; Carter and Poast 2017), crime (Getmansky, Grossman, and Wright

2019; Laughlin 2019), and terrorism (Thein 2004; Abrahams 2019). Despite their

prevalence, we know little about these barriers’ impacts. Beyond the simple question

of how well they prevent a specific type of movement across a specific location,

barriers may change the nature of illicit activity by shifting its location or tactics.

Walls’ unintended consequences are myriad (Carter and Poast 2020). Criminals may

find unguarded sections of borders to use for smuggling (Getmansky, Grossman, and

Wright 2019; Laughlin 2019), and illegal immigrants may cross a border via ports of

entry using forged documents if walls block other paths. To what extent do barriers

incentivize illicit actors to innovate or change strategies, and how do these changes

affect the nature of the underlying political problem?

We study the use of physical barriers to prevent terrorist violence, an outcome

which should be particularly susceptible to strategic innovation in response to wall-

building. Terrorists’ success is not tied to accessing a specific target with a specific

weapon. When government policies prevent access to preferred targets, terrorists can

shift their attention to a near-infinite selection of viable alternatives, or to a tactic

which is not stymied by a physical barrier (Enders and Sandler 1993; Powell 2007;

Brandt and Sandler 2010). Tilly (1993) notes that participants in insurrection select

new tactics from “repertoires of contention” in response to changing conditions.

Barriers which stymie existing tactics alter terrorists’ cost structures without chang-

ing their goals. Terrorists should therefore find new ways to achieve their goals that

are unaffected by physical defenses.

We test these arguments in the context of the “separation barrier” built by the

Israeli government in the early 2000s to prevent terrorists in the West Bank from

accessing targets in Israel Proper.

1

We operationalize variation in the barrier’s

porousness using the closures of checkpoints which regulate movement between

the two sides. On most days, checkpoints allow controlled access across the barrier,

providing opportunities for terrorists to sneak through. Periodic closures temporarily

reduce porousness, providing a counterfactual to the barrier’s presence which allows

us to evaluate its impact. Given that the timing of closures is endogenous to the

underlying threat of attack, we employ an instrumental variable, Israeli holidays,

which strongly predict checkpoint cl osures but are correlated with the threa t of

attack almost exclusively through changes in the barrier’s porousness.

Drawing on new data on the date, location, and weapon of every terrorist attack in

Israel and the Palestinian Territories between 2000 and 2017, we find that check-

point closures reduce the likelihood of at least one terror attack occurring on a date

by about 10.7 percentage points. However, there is some indication that sealing the

barrier delays rather than reduces attacks: when checkpoints are open, the highest

probability of attack comes immediately following a closure. These mixed impacts

of the barrier are exacerbated by changes in terrorist tactics and targets. Among

attacks that occur, a higher proportion use weapons of convenience like knives, cars,

and Molotov cocktails when the barrier is sealed, presumably because these weapons

are readily available on both sides. A higher proportion of attacks also use suicide

1132 Journal of Conflict Resolution 65(6)