Why Do Former Rivals Form Non-Aggression Pacts?

Non-aggression pacts, designed to reduce the possibility of future conflict, are distinctive from other military alliances because they do not necessitate active coordination between signatories. However, what they do have in common with other types of alliances is that they allow for the involvement of third parties. Besides recognizing mutual commitment to the prevention of future instability as one obvious reason for non-aggression pact formation, political scientists Yonatan Lupu and Paul Poast also cite the desire to credibly signal the end of a previous rivalry and to indicate peaceful intention to outside actors. In their recent paper, Lupu and Poast describe reasons why states use non-aggression pacts for signaling purposes.

The authors focus on the role of previous rivalry in non-aggression pact formation and the implications for outside actors. Although state leaders and inside actors of former rivalries may feel certain when the likelihood of future conflict has declined, actors on the outside, including domestic entities and other states, cannot so easily dismiss the threat. An ostensible absence of hostility alone may not eliminate the uncertainty about whether the rivalry has truly ended, especially since many ongoing rivalries do not manifest visible conflicts. Thus, leaders of states with recently concluded rivalries may capitalize on non-aggression pacts to help mitigate this uncertainty.

This argument begs the question of what benefits are gained from such informative signaling. The answer is multifold: Not only does it improve relations with states who previously sided with a past rival, but it can also open up the possibility of new economic and political connections. For instance, leaders of states that are close to one of the former rivals may not want to build relations with an opposing state unless a signal existed that the rivalry had finished and an amicable relationship would ensue going forward. Leaders of previously feuding states have ample incentive to offer this signal, lest they miss the opportunity to reap potential economic and political benefits.

The authors plotted non-aggression pact formation data between 1900 and 2001, drawn from the Alliance Treaty Obligations and Provisions (ATOP). Rendered in Figure 1*, a total of 137 non-aggression pacts were identified during the period. Most notably, this chart shows a rash of non-aggression pacts formed in the early 1990s when the Soviet Union collapsed. Russia, along with other former Soviet republics, and Eastern European states contributed to this spike. Another visible pattern is the consistency of non-aggression pacts formed after World War I and II. This suggests, and the authors hypothesize, that non-aggression pact formation is more prevalent among states that have recently resolved a conflict.

Deducing from the distribution of the 137 non-aggression pacts, the authors generated a realistically sized random sample of non-formations of non-aggression pacts: 10,531 observations in which a non-aggression pact was not formed between the same years. With formations and non-formations totaling 10,668 observations, the authors used network analysis to calculate the prevalence of rivalries that have ceased in the past ten years within groups of states. Based on these calculations, the authors show a positive association between non-aggression pact formation and recent rivalry cessation: The average value of the recent rivalry cessation prevalence for 10,531 observations in which a non-aggression pact was not formed was 0.007, while the average recent rivalry cessation prevalence of 137 observations in which a non-aggression pact was formed was 0.037.

To test this association more in depth, the authors incorporated several supplementary factors into their analysis: the presence of a common threat, state regime type (using Polity IV scores), similarity of foreign policies, geographic proximity, and national power (using the total Composite Index of National Capabilities (CINC) score.) All of these factors either positively or negatively influence the likelihood of a non-aggression pact formation. Based on these considerations, the authors apply several statistical specifications and find that groups of states with a higher prevalence of recent rivalry cessation are more likely to form non-aggression pacts. A state that has a prevalence (defined as one on the authors’ scale of zero to one) of rivalry cessations is more than five times as likely to form a non-aggression pact than one that has zero previous rivalry cessations.

These results support the authors’ argument that non-aggression pacts can be used not only as a commitment to peace, but as an instrument to signal this commitment to external actors. States are more likely to form non-aggression pacts if they have recently ended a rivalry as both domestic and international actors may have concerns that dormant conflicts may revive. Leaders of prior belligerent states can use non-aggression pacts to provide a material message that peaceful relations will continue. Considering the political and economic incentives that come with the end of hostilities, the authors indicate that many states form non-aggression pacts for a higher benefit than their initial face value.

*Figure 1 has been rendered with replication dataset files provided online by Paul Poast.

Article source: Lupu, Yonatan, and Paul Poast. “Team of Former Rivals: A Multilateral Theory of Non-Aggression Pacts.” Journal of Peace Research 43, no. 3 (2016): 344-358.

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