The relationship is robust, empirical, and reverse causal.

Contrary to van de Haar’s (2020) assertion that the will to truck and barter cannot overcome the will to make war, numerous empirical studies demonstrate the inverse relationship between trade and conflict (see Gartzke and Li 2003; Oneal 2003; Oneal, Russett and Berbaum 2003; Dorussen 2006; Xiang, Xu and Keteku 2007).3 In addition to trade, there is evidence that foreign direct investment and financial openness positively affects peace (Souva and Prins 2006, Kim 2014). Gartzke (2005, 2007, 2009) extends the argument that trade produces a marginal reduction in violence with evidence that economic freedom and financial market openness reduce the likelihood of war. Further, Gartzke (2007) and Gartzke, Li, and Boehmer (2001) find that capitalism is the causal mechanism behind the liberal peace. They argue that when accounting for the influence of capitalism on international relations, the influence of democracy disappears. Gartzke and Hewitt (2010) analyze the effect of capitalism and democracy on crisis intensity, escalation, and longevity, finding support for the capitalist peace. Importantly, they find that democracy has no significant, independent effect on interstate crisis behavior.

McDonald (2009) finds that “First, liberal economic institutions promote peace. Second, these economic institutions have historically played a stronger role in promoting peace than democracy” (p. 281). He also finds that “public property heightens the likelihood of military conflict for all regime types” (p. 276). Public property and resources enable a ruler to pay for foreign policy irrespective of the wishes of taxpayers and opposition from other governmental actors. Moreover, large portions of public property can sustain arms races that shift the balance of power and tempt preventative strikes. McDonald (2010) also finds support that capitalism, relative to democracy, plays a larger role in limiting violent conflict between states.

Subsequent work has extended dyadic capitalist peace arguments to include the impact of participation in a broad trade network and specific international organizations. Membership in multilateral organizations further strengthens economic ties and contributes to the capitalist peace. Strong trade relations between states are the most critical determinant of joint participation in Intergovernmental Organizations (IGOs) (Boehmer and Nordstrom 2008). In a series of studies, Dorussen and Ward (2008, 2010, 2011) focus on the pacifying impact of the connections and communication that result from trade. They hypothesize that as the number of indirect trade links a dyad shares with a third party increases, the likelihood of conflict decreases. Empirically, they find that as the world has become more connected through dense trade networks, the importance of general engagement with the global trade network has grown larger than trade links with particular third parties.

Building on Dorussen and Ward’s claim that links to third parties and the global trade network decrease conflict, Peterson (2011) addresses the counterfactual that third-party trade can increase conflict. He argues that third-party trade among states with conflicting strategic interests may threaten the stability of the dyadic power balance encouraging militarized disputes. However, he finds that the aggravating impact diminishes in dyads with shared state preferences or a high degree of mutual embeddedness in trade networks.

In a corollary to Peterson (2011), Peterson (2015) argues that when one member of a dyadic trade relationship enters into a Preferential Trade Agreement (PTA) that reduces the exports of the nonmember, at least relatively, the nonmember will perceive a threat. Thus, he examines PTAs as a predictor of conflict between dyads where one state is excluded. This illustrates the importance of inclusiveness in trade—when parties are excluded from agreements fostering free trade it can increase the chance of conflict.

World War I is often raised as a challenge to the idea that economic interdependence discourages violence as a means of conflict resolution. Gartzke and Lupu (2012) offer a different interpretation. They analyze the two economic subsystems of Europe to argue that the less interdependent portions of Europe from 1871-1913 moved the continent toward war. In contrast, in the decades prior to World War I the more interdependent European powers were able to resolve crises without resorting to war. They conclude that “in contrast to conventional wisdom, the 1914 crisis is a particularly weak case against commercial liberalism” (Gartzke and Lupu 2012, p. 149).

Michael Mousseau has produced two decades of work finding that democracy is a significant force for peace—but only in wealthy dyads (Mousseau 2000, 2005; Mousseau, Hegre and Oneal 2003). He has also studied the impact of contract-intensive economies on peace. A contract-intensive economy refers to a society where individuals largely rely on trade with strangers through markets. This stands in contrast to contract-poor societies where people largely engage with a small group of people with strong social ties (e.g., family, friends, religious community). Mousseau (2009) finds that for the 1961-2001 period there were no fatal conflicts among nations with contract-intensive economies. He also finds that contract-intensive economies prefer peace to war—for the 1961-2001 period there was no civil war, insurgency, or rebellion in any nation with a market-capitalist economy (Mousseau 2012)—providing further support that the capitalist peace supersedes the democratic peace (Mousseau 2018, 2019).

What about the non-economic aspects of markets? McCloskey (2006, 2010, 2016) offers historical evidence from seventeenth- and eighteenth-century Europe that while virtues are necessary for functioning markets, “the market supports the virtues” (2006, p. 4). The seven virtues of the commercial society, McCloskey argues, are love, faith, hope, courage, temperance, prudence, and justice. In her telling, markets offer a space for the virtues to evolve and flourish and are central to explaining the wealth and stagnations of societies. Storr and Choi (2019) provide additional evidence concluding that “Beyond exhibiting the seven virtues that McCloskey highlighted ... we show that people in market societies tend to be more altruistic, are less likely to be materialistic and corrupt, and are more likely to be cosmopolitan as well as trusting and trustworthy” (p. 13). Moreover, they argue that markets are spaces that can make people more moral through their interactions with others.