Mowing the grass
| Published date | 01 July 2023 |
| DOI | http://doi.org/10.1177/09516298231185113 |
| Date | 01 July 2023 |
| Subject Matter | Articles |
Mowing the grass
Michael Gibilisco
California Institute of Technology, Pasadena, CA, USA
Abstract
Mowing the grass is a cyclical pattern in counterterrorism campaigns where governments attack to
destroy terrorist capacity, thereby achieving a period of quiet as groups recover. If groups expect
their capacity to be destroyed, why build their capabilities in the first place? I analyze an infinite-
horizon dynamic game where a group endogenously builds capacity in the face of potential attacks
and capacity is an evolving, persistent variable. The model highlights that terrorist groups and gov-
ernments have incentives to create strategic uncertainty and thus explains attack cycles without
punishment strategies, revenge preferences or imperfect/incomplete information. I calibrate the
model to time-series data in the Israeli–Palestinian conflict describing rockets fired from Gaza.
The results illustrate a peace-making dilemma: altering the government’s incentives will have com-
paratively minimal effects on long-term conflict dynamics, whereas changing the terrorists’incen-
tives to acquire capacity would either increase the frequency of high-capacity terrorism or
government attacks.
Keywords
Counterterrorism, group capacity, Israeli–Palestinian conflict, model calibration, terrorism
1. Introduction
Mowing the grass refers to a cyclical pattern in counterterrorism campaigns: the terrorist
group builds its capacity for violence, and once it becomes too strong, the government
attacks to destroy this capacity. Eventually the group rebuilds, and the process repeats.
The phrase is associated with the Israeli-Palestinian conflict after the Israeli Defense
Force (IDF) launched Operation Protective Edge, a military incursion into the Gaza
Strip aimed at stopping Hamas rocket fire into Israel (Inbar and Shamir, 2014). The
pattern also appears more broadly. The Obama and Trump administrations used the
Corresponding author:
Michael Gibilisco, Division of Humanities and Social Sciences, California Institute of Technology,
1200 E. California Blvd., MC 228-77, Pasadena, CA 91125, USA.
Email: michael.gibilisco@caltech.edu
Article
Journal of Theoretical Politics
2023, Vol. 35(3) 204–231
© The Author(s) 2023
Article reuse guidelines:
sagepub.com/journals-permissions
DOI: 10.1177/09516298231185113
journals.sagepub.com/home/jtp
phrase to describe U.S. operations against terrorist organizations in Africa and Asia
(Snow, 2019; Bowden, 2021).
When both the government and the terrorist group comprehend each other’s behavior
and the larger fundamentals of conflict, mowing the grass highlights a strategic tension. If
terrorist groups anticipate the attacks that would arise if they increase their capacity, why
build up capabilities that will only be destroyed? In contrast, mowing the grass is suppose
to be a cost-effective counterterrorism strategy, where government attacks generate a
period of extended peace. If the government anticipates that the group will immediately
rebuild, why continue to attack when it means exerting costly effort to attack again?
In this article, I study this strategic environment using a dynamic game with endogen-
ous group capacity. The game has three key features that are essential to the
mowing-the-grass metaphor. First, when the terrorist group invests resources to increase
its capacity, the government observes the resulting investment before it decides to attack.
That is, the mower can watch the grass grow. Second, capacity is persistent in the sense
that once the group acquires capacity, it persists until the government takes costly action
to destroy it. That is, the grass does not mow itself. Third, the interaction has an infinite
horizon. That is, the grass at least has the opportunity to regrow.
This stylized model elucidates the dynamic tradeoffs underlying mowing the grass.
When costs are large enough such that the actors cannot commit to attack or invest in
every period, the government only attacks if it expects the group to not immediately
rebuild. Likewise, the group only builds its organizational capabilities if it expects the
government to not respond immediately with attacks. Thus, the group’s dynamic benefits
of acquiring capacity intimately depend on its expectations about the frequency of gov-
ernment attacks, and the government’s dynamic benefits of attacking depend on its
expectation about how quickly the group rebuilds. As such, multiple equilibria exist.
In the deterrence equilibrium, the group never invests in its capacity, and the government
always attacks groups with high capacity. In the rampant-terrorism equilibrium, the group
always invests and the government never attacks. In the mowing-the-grass equilibrium,
the group randomizes its investment decision and the government randomizes its
attack decision.
The mowing-the-grass equilibrium, therefore, rationalizes cycles of government
attacks and the evolution of terrorist capacity over time. It emerges under relatively
stark conditions that do not require punishment strategies, incomplete or imperfect infor-
mation, revenge preferences, or exogenous stochastic forces, which are other explana-
tions for the patterns. It also produces novel comparative statics. In equilibrium, the
government attacks high-capacity groups with probability that makes low-capacity
groups indifferent between building capacity and not. When the cost of building capacity
increases, the government’s equilibrium probability of attacking decreases thereby
increasing the dynamic benefits of acquiring capacity and compensating the group for
its larger investment costs. Thus, higher investment costs increase the long-term probabil-
ity of high-capacity terrorism and increase the time between government attacks. For
similar reasons, as the government’s cost of attacking increases, the terrorist group’s equi-
librium probability of investing in its capacity decreases, which leads to less high-
capacity terrorism and longer times between government attacks.
Gibilisco 205
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