In recent years, a renewed interest in the differences between dyadic conflicts and complex, multiparty disputes has developed within international relations (Vasquez and Valeriano 2010; Valeriano and Vasquez 2010). The conflict expansion literature focuses heavily on how traditional realist variables – such as alliances, shared borders, and rivalries – facilitate the spread of conflict, but these studies largely ignore other incentives to join disputes, such as the protection of an economic relationship. Absent a few notable exceptions (Polachek 1980; Aydin 2008), questions concerning the role that economic interdependence plays in conflict expansion have remained generally unanswered.

This dissertation seeks to address the economic incentives to join ongoing disputes. Are states likely to join into conflicts as third parties to protect their economic relationships? I approach this question in three parts. First, I investigate states’ conflict-joining propensities with regard to bilateral trade ties, making note of the evolution of the international economy from 1885-2001. I find that states are more likely to join disputes at higher levels of trade dependence and higher levels of trade concentration, but where the economy is more liberalized, the probability of joining is lower even at high values of trade dependence.

Second, I investigate whether states that abstain seek alternative markets to substitute trade jeopardized by the outbreak of a trade partner’s conflict. States might do this to avoid conflict participation and also to ensure that their own economic health is preserved. If such circumvention occurs, then we should expect trade values to fall between a state and its disputatious trade partners, while trade values between non-disputant trade partners should simultaneously rise. I do not find support for these hypotheses.

Finally, I question not only whether states are willing to skirt conflict by diverting trade, but also whether they can. Here I assess how different trade components affect the probability of military intervention, arguing that the unique nature of primary commodities renders these goods virtually non-substitutable. Because of this, third parties whose economies rely heavily on trade in primary goods are more likely to intervene to protect their lifeline of resources. I find some support my primary hypotheses.