The effects of shocks on international networks
| Author | Kyle A Joyce,Zeev Maoz |
| Published date | 01 May 2016 |
| Date | 01 May 2016 |
| DOI | http://doi.org/10.1177/0022343316632854 |
| Subject Matter | Research Articles |
Research Articles
The effects of shocks on international
networks: Changes in the attributes
of states and the structure
of international alliance networks
Zeev Maoz
Department of Political Science, University of California, Davis & Interdisciplinary Center, Herzliya
Kyle A Joyce
Department of Political Science, University of California, Davis
Abstract
We study the effects of shocks – such as major wars that change states’ strategic environments – on alliance networks.
This has important implications for the structure of security cooperation networks. We develop an agent-based model
(ABM) that: (1) models network evolution processes of security cooperation networks; (2) induces shocks that cause
significant changes in agents’ utilities due to shifts in common interests between states; (3) analyzes how networks
reorganize in the post-shock period. We derive propositions from the ABM about the relationship between shock
attributes and network structure. We compare the results of the ABM to similar shocks that operate on real-world
alliance networks. The ABM results with random network data suggest that states that experience dramatic changes in
their strategicenvironment increase networkconnectivity and consistency.Consequently, post-shock networks become
increasinglyconnected (denser) and consistent (transitive). With a few notable exceptions, these resultsare corroborated
by analysis of alliance network reorganization following shocks. We discuss the theoreticaland empirical implicationsof
the results and offer directions for future research on shocks and international networks.
Keywords
agent-based models, alliance networks, homophily, network connectivity, network consistency, network
reorganization, shocks
‘We [England] have no eternal allies and we have no
perpetual enemies. Our interests are eternal and perpe-
tual, and those interests it is our duty to follow.’
Lord Palmerston, remarks in the House of Commons,
1 March 1848.
Introduction
Major international conflicts can cause leadership turn-
over (Bueno de Mesquita, Siverson, & Woller, 1992;
Chiozza & Goemans, 2004), drastic changes in economic
growth (Organski & Kugler, 1980), territorial change,
and population shifts (Diehl & Goertz, 2000). Some con-
flicts have structural effects on the international system
(Brecher, 2008; Gilpin, 1981). International conflicts
alter the challenges to states’ security and the structure
of their interests. Yet, we have limited knowledgeon how
such shocks affect behavior, and the implications for the
structure of international networks.
To motivate this study we show in Figure 1 how
shocks have influenced alliance neworks over time. Some
shocks (e.g. World War II) have a brief, spike-like effect
on the density of alliance networks, with density quickly
returning to a stationary equilibrium. However, shocks
Corresponding author:
zmaoz@ucdavis.edu
Journal of Peace Research
2016, Vol. 53(3) 292–309
ªThe Author(s) 2016
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DOI: 10.1177/0022343316632854
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had a lasting effect on alliance polarization (i.e. the
degree to which the network approaches strict bipolar-
ity), producing a new trend or equilibrium.
Consider two critical turning points in international
history: the end of World War II, and the end of the
Cold War. During WWII, the USA and Great Britain
formed an alliance with the Soviet Union against Ger-
many. Once the war ended and tensions between the
former allies increased, the Western states formed
NATO and the Soviets formed the Warsaw Pact. Former
enemies – the United States and Japan and France and
Germany – became allies, and former allies – the United
States and China – became adversaries. The collapse of
the Warsaw Pact at the end of the Cold War was fol-
lowed by the expansion of NATO, with some Eastern
European states joining their former adversarial alliance.
Here too, former adversaries became allies, and former
allies (i.e. the new Eastern European NATO members
and Russia) became potential adversaries.
Our study centers on the way shocks – events that
cause dramaticchange in states’ interests – affect the struc-
ture of alliance networks. Specifically, we study how these
shocks – changesin the identity of shared enemies – affect
the propensity of states to form or break alliances, and the
network implications of such decisions. The following
questions guide the present study:
(1) How do shocks affect alliance network
reorganization?
(2) What is the relationship between the character-
istics of a shock (e.g. size, spread, magnitude)
and the structure of post-shock network
reorganization?
We employ a two-step strategy. First, we develop an
agent-based model (ABM) that simulates network for-
mation and network evolution processes. The ABM
enables us to deduce hypotheses on how shocks affect
international networks. Second, we test these hypotheses
by comparing the ABM results to the effects of shocks on
real-world security cooperation networks.
Most studies of shocks in networks focus on network
resilience. By contrast, the innovation of our study is in
showing how shock characteristics (e.g. size, spread,
magnitude) affect network reorganization. This is done
by comparing the pre-shock structure of networks to
their post-shock structure, and by comparing the results
of an ABM with random network data to real-world
0 .05 .1 .15 .2 .25 .3
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Year
Polarization Density
Seven-Week
War (1866) World War I
(1914-18)
World War II
(1939-45)
End of Cold War
(1988-91)
Collapse of Spanish
empire in South Am.
(1823)
Figure 1. The polarization and density of international alliance networks, 1816–2004
Sources: Leeds, 2005; Maoz, 2010.
Maoz & Joyce 293
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