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Are Alliances a Prerequisite for Multiparty War?

The following analysis is from Volume 2, Issue 1 of the Peace Science Digest. 

The scientific study of war has shown that alliances between countries cause an initial expansion of a war. This research explores more deeply whether alliances are a necessary condition for large, multiparty wars, as well as the role political rivalries play in the development of multiparty wars. Alliance-making institutions such as the North Atlantic Treaty Organization (NATO) are also an important factor in the creation of large wars. The authors point out that membership in certain institutions creates a web of incentives and punishments that can force a country to do things it might not do if it were not a member of that institution, and that without the institution of alliances large wars would not occur.

The authors define multiparty wars as wars with three or more states [countries], which often occur when one of the two original countries in conflict feels it cannot defeat the other alone. A database was analyzed to review every interstate war from 1816 to 2007 and establish if the warring parties were preceded by alliances. The database lists each party in the war, when they joined the war, and whether they were allied with another party before the war broke out. The research team used this data to seek support for the following hypotheses:

  1. Prior alliances are necessary conditions for multiparty wars and will precede most multiparty wars.
  2. Rivalries and shared borders are not necessary conditions for war and will not precede most multiparty wars.

To test the first hypothesis, the authors examined each interstate war in the database with more than two parties to see whether it was preceded by one or more alliance(s). The database provided information on 35 multiparty wars and 55 dyadic wars (wars between two countries). It was necessary to compare multiparty wars with dyadic wars to determine if alliances are specifically associated with multiparty wars. To test the second hypothesis, the researchers first needed to establish measures for ‘rivalries’ and ‘shared borders’. To qualify as rivals, two countries must have had three or more ‘militarized interstate disputes’ (MIDs), or past armed skirmishes. To qualify as having a shared border, countries must share a land border or river.

The results of the authors’ research supported their hypotheses. Prior alliances were found in 91% of all multiparty wars, compared to just 58% of dyadic wars—supporting their first hypothesis that prior alliances are a necessary condition for multiparty wars. Alliances were also found to increase in necessity as the scale and size of the war increased, a finding exemplified by the two World Wars. World War I had a total of 37 participating countries, and all but one held alliances prior to joining the war. World War II had 79 participants, with every country holding at least one alliance prior to joining the war. The World Wars exemplify the authors’ findings, showing that the larger a multiparty war is, the more likely prior alliances are to be found among the war’s participants.

The authors’ analysis on rivalry and shared borders found that two-thirds of multiparty wars were preceded by rivalries, far less than what is needed to accurately label rivalry as a necessary precondition. The same was true with the borders of participants in multiparty wars—only 60% of warring countries shared borders with another participant. These findings supported the second hypothesis that rivalries and shared borders are not necessary conditions of war.

These findings provide the opportunity to examine how treaty and alliance organizations can contribute to war and spread war’s burden to countries that would otherwise refrain from participation. The authors highlight the United States’ involvement in the Korean War, for example, and how the country dragged 17 North Atlantic Treaty Organization (NATO) members into a war that they would most likely not have participated in had it not been for the treaties and alliances binding them to the United States. More recently, the United States led NATO Coalition Forces of over 23 countries during the wars in Iraq and Afghanistan—wars that were solely initiated by one country but, due to NATO alliances, burdened dozens more with the human and economic costs. Without the majority funding and political authority from nations like the United States, alliance organizations like NATO would not exist. Therefore, further examination into the efficacy of wealthy nations bankrolling these organizations is warranted.

Contemporary Relevance:

NATO forces are currently involved in various capacities in Afghanistan, Kosovo, Somalia, the Mediterranean Sea, Russia/Ukraine, Albania, Slovenia, and areas in the Baltic. Although almost all their membership is European and most of their security engagements are in Europe, NATO does not reflect an institution of equals. Rather, NATO military action is initiated by the U.S. and followed by its European members. NATO is also unequipped to confront most of today’s security issues. They have been unable to effectively respond to the ongoing refugee crisis, Ukraine is still on standby, the Taliban are spreading in Afghanistan, and they have done nothing to curb or prepare for the effects of global warming, which many say is humanity’s most pressing security threat. One has to question whether such military alliances have a place in the contemporary world. where viable nonviolent alternatives to military intervention exist. NATO is without doubt a leftover from the Cold War which currently reinforces the war system and plays a role reigniting a new Cold War with the potential for escalation.

Practical Implications:

Alliance organizations justify their existence partially to deter or intimidate countries from going to war with an allied member. The findings of this research should be used to encourage a discussion on the effectiveness and morality of alliance organizations. Organizations such as NATO were developed to provide collective defense for members. However, if a conflict leads to a war that could potentially drag dozens of neutral countries into battle, then such organizations may be counterproductive. Instead, political leaders, NGOs, and independent activists should petition their governments to strengthen their support for supranational governance organizations such as the United Nations (UN) and the European Union (EU), rather than falling back on antiquated systems of military alliances that seem to offer more risk than they do security. The ‘soft power’ of the EU has already seen success in their role in Georgia and stabilizing the Balkans; this model should be replicated in the future instead of NATO pulling more countries into war.

Talking Points:

  • Alliances are a necessary condition for multiparty wars.
  • The larger the war, the more likely alliances are a necessary condition.
    • 95% of WWI participants and 100% of WWII participants held prior alliances.
  • Prior rivalries and shared borders are not necessary conditions for multiparty war


Vasquez, J. A., & Rundlett, A. (2016). Alliances as a necessary condition of multiparty wars. Journal of Conflict Resolution, 60(8), 1395-1418.

Continued Reading:

  • Should NATO Be Handling World Security? By Lawrence S. Wittner. 2012.
  • NATO’s Dangerous Game: Bear-Baiting Russia. By Conn Hallinan. 2016.
  • Is NATO Obsolete? By Jonathan Power. 2017.
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