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Van Evera: Offense, defense, and the causes of war

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Van Evera. 1998. Offense, defense, and the causes of war. International Security 22 (spring): 5-43.

MAIN ARGUMENT: "war is far more likely when conquest is easy... shifts in the offense-defense balance have a large effect on the risk of war" (5). The shifts in the offense-defense balance can be either real or perceived, but shifts will affect the likelihood of war.

Y = War (the costs and benefits of war, to be more specific)

X = the offense-defense balance

DETERMINANTS of the Offense-Defense Balance:

  • Military Technology and Doctrine: military technology can favor either the aggressor or the defender.
  • Geography: conquest is more difficult when states are geographically insulated from invasion or strangulation.
  • Social and Political order: popular regimes are generally better at conquest and self-defense than unpopular ones.
  • Diplomatic arrangements: three types of diplomatic arrangements strengthen the defense: collective security systems, defensive alliances, and balancing behavior by neutral states.

THEORY: Offense-Defense's Ten Explanations for War

  • Opportunistic Expansionism: when conquest is hard, aggression is dissuaded by the fear that victory will be too costly
  • Defensive Expansionism and Fierce Resistance to expansionism: when conquest is hard states with secure borders are more willing to accept the status quo.
  • Moving first is more rewarding
  • Windows are larger and more dangerous
  • Faits accomplis are more common and more dangerous
  • States negotiate less and reach fewer agreements: states let more disputes fester when the offense dominates
  • States are more secretive: information advantages lead to rewards
  • States Arms Race Harder and Faster: when defense dominates you get a "virtuous cycle" [shouldn't that say "vicious cycle"?]
  • Conquest grows still easier: offense dominance is self-reinforcing.


Van Evera uses three case studies to check whether the predictions of Offense-Defense hold up empirically. He studies: Europe since 1789, ancient China during Spring and Autumn and Warring States eras, and the US since 1789. He claims that these cases all show variation in the (real or perceived) offense-defense balance (IV). He admits that the Chinese case study is weak, but pins it on lack of knowledge. However, Van Evera claims that the overall indications of the three studies combined support the theory.