Democratic Peace Theory, Power, and Economic Interdependence

Synthesising Democratic Peace Theory with Concepts of Power and Economic Interdependence

Democratic Peace Theory has been referred to as the “closest thing we have to an empirical law in the study of International Relations” (Levy 1989: 88). The evidence certainly suggests that liberal democracies rarely, if ever, go to war with each other (Owen 1994, Dafoe et al 2013). However, Democratic Peace Theory (hereafter referred to as DPT) has come under much criticism for a variety of reasons. These challenges have predominantly centred around three strands. Firstly, that the definition of a liberal democracy is unclear and inconsistent. Secondly, that the causal logic of DPT is flawed. Thirdly, that realism still provides a better explanation for peace between liberal democracies.

This essay will argue that DPT provides a satisfactory explanation for the peace that exists between liberal democracies, however, it will also suggest that a synthesis between DPT and the arguments of its critics can actually make it stronger and more convincing. To properly account for peace between liberal democracies such a synthesis is necessary, and possible. To reach this conclusion this essay will firstly explore the definition of a liberal democracy and will analyse the criticisms DPT receives in this area. Secondly, it will analyse the allegedly flawed causal logic of DPT. Thirdly, it will analyse Realist claims that concepts such as power can explain the liberal democratic peace. Finally, it will show that a synthesis of DPT with concepts of power and economic interdependence can strengthen the argument.

Definitional issues Surrounding Democratic Peace

“How does one define democracy? What counts as a war?” (Owen, 1994: 87). These questions are fundamental in establishing what is meant by ‘democratic peace’. Spiro challenges DPT on the very fact that the theory is “entirely dependant on tricky and highly contestable definitional issues” (Russet et al 1995). Although detailed definitions vary between scholars, there is a general consensus on what a ‘liberal democracy’ is. A liberal democratic state should consist of: freedom and protection of individuals in society, a common legislation that is equal for all, free speech and competitive elections, and a dominant liberal ideology (Kant 1795, Doyle 2005, Owen 1994). However, the definition of ‘war’ is more contested. Whilst DPT advocates claim that no two democracies have ever been to war, Layne (1994: 16) argues that they have on several occasions, for example during the Anglo-American Trent Affair in 1861, which by the standards of Small and Singer (1982) would be considered a diplomatic crisis rather than a war. Small and Singer define war as multilateral violence between two or more states with at least 1000 combat troops involved or at least 100 combat related casualties.

Although these proposed definitions of liberal democracy and war combine to provide a thorough definition to underpin (and challenge) DPT, the problem is that not all scholars use them. Until both advocates and opponents of DPT agree to a common definition, it will be hard for either side to make progress when critics can disregard much of each other’s arguments from the offset.

To further complicate the matter of inconsistent definitions, Owen (1994) raises the idea that perception counts for as much as a definition. He argues that it is insufficient for a state to simply be a liberal democracy, it must also be perceived as one. He uses the example that France did not consider Germany to be a liberal democracy after the First World War, even though the Weimar Constitution was liberal. “Thus, for the liberal mechanism to prevent a liberal democracy from going to war against a foreign state, liberals must consider the foreign state a liberal democracy” (1994: 96, emphasis added). This argument is persuasive, and goes some way in explaining why a consistent definition is perhaps non-essential – as even an objective definition will be interpreted subjectively by states, according to their outlook on other states.

Although many critics of DPT use definitional issues as part of their argument, it is worth noting that they too are subject to such error. Just as no common definition is used by advocates of DPT, neither is one used by the opposition. Owen admits that definitions adapted to fit the argument are a valid challenge to DPT, but that “critics are also susceptible to the tautological temptation” (1994: 88). Therefore it can be concluded that although the credibility of DPT suffers from a lack of a clear, consistent definitions for ‘liberal democracy’ and ‘war’, this is not sufficient to damage the theory itself. Opponents are just as susceptible to the same errors, and regularly do so. Although it would be unrealistic to say that errors on both sides simply cancel each other out, the definitional challenge does not have enough substance to threaten the core of DPT.

Flawed Causal Logic of Democratic Peace Theory?

The causal logics of DPT come in two strands, institutional and normative. The institutional argument states that should citizens deem the cost of war to be too high, then they have the power to prevent it, through electoral leverage over their authorities. Furthermore, democracies have ‘checks and balances’ in place, in the form of “executive selection, political competition, and the pluralism of the foreign policy decision making process” (Layne 1994: 9), which constrains the power of individuals in authority (Doyle, 1986). The normative argument states that liberal democracies have a domestic culture of non-violent conflict resolution, which is externalised through foreign policy and leads liberal democracies to trust and respect each other. Through a process of perception and cooperation, liberal democracies accommodate each other to expand beneficial international relations (Doyle, 1986).

Critics of DPT argue that whilst empirical evidence certainly points towards general peace between democracies, the causal logic of the theory is flawed (Rosato 2003, Layne 1994). For a theory to be compelling, the evidence must support the chain of causal mechanisms (Rosato 2003). This certainly holds true, and all advocates of DPT would agree.

The institutional causal logic is challenged by Layne. He argues that “institutional constraints do not explain the democratic peace. If democratic public opinion really had the effect ascribed to it, democracies would be peaceful in their relations with all states, whether democratic or not” (1994:12). What Layne fails to consider however, is the impact that liberal ideology has on public perception. An enlightened population living in a liberal democratic state will appreciate the value of other enlightened populations who adhere to the same ideology (Kant 1795, Doyle 2005). Assessing the cost of war is the primary concern of citizens, but it is not the only one. The shared ideology of citizens in liberal democracies makes them much more accommodating of each other than with non liberal states. Therefore institutional constraints are not solely based on the cost of war, but also have a consideration for similar patterns of belief. Furthermore, Layne attempts to prove that public opinion is not always an inhibitor of war, using the example that in 1914 “war was enthusiastically embraced by public opinion in Britain and France” (1994: 12). Firstly, in 1914 Germany was certainly not perceived by Britain and France as being a liberal democracy, and secondly, the public would most likely have perceived the cost of not going to war to be greater, as a spread of illiberal power in Europe would have eventually challenged these states’ own liberal ideology. Layne’s challenge to institutional causal logic does little, if nothing, therefore, to challenge DPT.

An argument against the normative causal logic of DPT is put forward by Rosato, stating that “democracies do not reliably externalize their democratic norms of conflict resolution, nor do they generally treat each other with trust and respect when their interests clash” (2003: 588). Although Rosato (2003) references examples between 1838 and 1920, more recent events appear to give his argument some weight. The alleged US spying in Germany, for example (BBC News 2014), seems to prove a lack of trust between two of the most liberal democratic states, and not even at a time when their interests clash. He concludes that if DPT is correct, liberal democracies should only fight wars out of self defence or to protect human rights. Kinsella offers a rebuttal to this argument, stressing that “democratic restraint is conditioned on expectations about the conduct of the other party in the interaction, expectations informed by the other’s internal political processes” (2005: 453). Without knowledge of these processes the cases that Rosato offers cannot be considered anomalies. Furthermore, Owen’s (1994) argument about the importance of perception could eliminate some of Rosato’s examples, as many of the states he lists could be perceived as being either illiberal or undemocratic. Although Rosato’s argument is hard to prove, it does make sense according to a realist line of thought, that states ultimately act out of self interest, regardless of internal domestic make up. Therefore the normative causal logic of DPT isn’t without challenge.

The issue with the arguments put forward by Layne and Rosato is that they both attack individual strands of the causal logic of DPT, ignoring the fact that several advocates of the theory emphasise that all the causal mechanisms must work together, and not separately (Doyle 2005, Russett 1995). Alone they do not hold up, but taken together, they become effective. Owen (1994) goes one step further, actually claiming to have found flaws in both the normative and institutional causal logics when taken separately, finding similar results to that of Rosato (2003). He found that “democratic structures were nearly as likely to drive states to war as to restrain them from it” and that “normative theory neglected to take perceptions into account” (1994: 91). He goes on to state that such typology is simply used for analytical convenience, and in no way concludes that DPT is flawed. Expanding on this, Doyle argues that “the three causes [explain] liberal peace and liberal war when, and only when, combined. Rosato’s critique of the work, nonetheless, rests on treating each of these factors… in isolation as if they were sufficient”. (2005: 463, emphasis added). It can be concluded then, that although there are flaws with both the normative and institutional causal logics of DPT when taken individually, these arguments no longer hold up when considered together. DPT is a multifaceted theory engaging with both ideology and domestic/international political institutions, and the two cannot be separated.

Realist Alternatives to Democratic Peace Theory

“The theoretical edifice of realism will collapse if attributes of states’ political systems are shown to have a major influence on which states do or do not fight each other” (Russett et al 1995: 164). Many of realism’s key concepts would be uprooted by the presence of a peace between liberal democracies. Whilst Liberals acknowledge the state of anarchy in which we live in, they stress that cooperation between states is possible, and that although peace is not the natural state of man, war can be averted through mutually beneficial interdependence (Kant 1795). For Realists however, power and self preservation are the driving factors of international relations, meaning that the domestic construction of a state has no impact on the way it conducts it’s foreign affairs. Only temporary peace can exist, when states balance power. If the ideological make up of a state does alter the way in which it interacts with other states, it would seem Realism cannot explain this. Therefore many of the criticisms of DPT are based on Realist approaches.

Neo-realists such as John Mearsheimer (1990) argue that the causal mechanisms suggested by DPT are simply impossible. He claims that even liberal democracies cannot trust each other, as there is always a possibility of sliding back into an authoritarian regime. If this is the case, then the security dilemma still exists because states must still worry about “relative power among themselves, which is tantamount to saying that each has an incentive to consider aggression against the other to forestall future trouble” (1990: 50). Mearsheimer continues, to explain that Britain and the USA allied themselves not because of a shared ideology, but due to the presence of a common enemy in Germany. These arguments are not persuasive. Although there is the possibility that some liberal democracies could slide back into authoritarianism, the rapid growth in the number of democracies in the 1990s would suggest otherwise. Furthermore, Owen (1994) suggests that Realism provides no explanation for why Britain decided to ally with the USA rather than Germany. Both the USA and Germany would have made formidable enemies, so it seems likely that a shared ideology was in fact what drew the two liberal democracies together. To further contradict the Realist perspective, the increase in democracies and consequent decline in autocracies would imply, according to the logic of Gartzke & Weisiger (2013), that some form of autocratic alliance would have emerged, creating an ‘autocratic peace’, which has not happened. The inability of Realism to ‘look in’ on the state leaves it partially blind when trying to explain how alliances are formed.

In more recent writing, Mearsheimer puts forward a persuasive argument for the still dominance of neo-realism. He analyses the 2014 Ukraine crisis and Russian annexation of Crimea, concluding that the continued expansion of NATO and the EU eastwards provoked Russia into a military response (2014). Although he does not explicitly make reference to DPT, he implies that a democratic peace cannot exist, continued expansion of NATO as a military alliance is proof of this. Once again however, Owen’s (1994) argument that perception must be taken into account is valid here. Western Europe and the USA do not view Russia as a ‘liberal’ democracy, explaining their somewhat hostile approach to dealing with a perceived illiberal Russia.

Another possible realist explanation of DPT could be that American dominance has created a zone of peace. Rosato concludes that “one possible explanation is that the democratic peace is in fact an imperial peace based on American power” (2003: 599). Many of DPT’s advocates base their research purely on examples of US relations with other states (Owen 1994). This limited scope of analysis means that the explanations provided for DPT could simply be due to American military and economic dominance. Although this argument is particularly persuasive in the post Second World War era, and especially in the post Cold War era, the USA has not always been a global hegemon, meaning that American military and economic prowess are unlikely the reasons for peace between liberal democracies (who tend to be allied to the USA). If not due to American power, then American ideology – liberal ideology – is more likely the reason for peace between liberal democracies.

Synthesising Democratic Peace Theory and Realism

Initially then, it would seem that DPT and Realism are locked in a head to head battle, where neither party can give ground. However there is a strong possibility that the two can be somewhat combined in order to provide the most persuasive argument for peace between liberal democracies. Many advocates of DPT do not dismiss Realism. In fact, many of them accept that even in liberal democracies power politics still play a role in shaping foreign policy (Owen 1994, Russett et al 1995, Keohane & Nye 1987). The key is that they accept power politics as part of a larger picture, whereas Realists see it as the essential component of international relations. Russet concedes that he is “happy to grant that power and strategic interest greatly affect the calculations of all states, including democracies” (Russett et al 1995: 166). For Owen, “both camps are describing real forces in international politics, namely, power politics and liberal ideas” (1994: 122). If both power politics and liberal ideology are accepted together as concepts that impact on liberal democracies, the arguments for democratic peace become much stronger.

Furthermore, DPT seems to be able to work with Walt’s Realist balance-of-threat theory. Walt (1987) stresses that states form alliances based on a perception of how aggressive the state is, not simply on perceptions of power and geographical proximity. This suggests that the domestic make up of a state actually plays a key role in how states decide to ‘balance power’. Therefore, if liberal democracies perceive each other as being pacific because of the institutional and normative explanations previously addressed, there is a convincing argument that the promotion of liberal ideology will lead to the spread of peace, as states will view each other as pacific and be more likely to form alliances than they would with an illiberal state.

There is also an important economic aspect to the fusion of DPT with Realism. Mousseau (2013), argues that rather than a democratic peace, there exists an ‘economic peace’ between what he calls ‘contract intensive’ states. Contract intensive economies (featuring an impersonal market) require a strong state, and have few motives to engage in war. This is because (in a similar fashion to the Liberal argument) contract intensive states have a “principle interest in the public good of ever expanding growth in the market” (2013: 189), as this create the most wealth, and as Keohane & Nye (1987) have shown, war has become increasingly costly for liberal democracies. The argument is very persuasive, and can be linked to DPT. It could be argued that contract intensive states can only fully develop in liberal democracies, as a thriving free market is one element of Liberal economic ideology. Furthermore, Keohane & Nye in their theory of interdependence (1987) elaborate on the benefits of economic interdependence between states. They do not challenge Realism, but state that “patterns of interdependence and patterns of potential power resources in a given issue-area are closely related – indeed two sides of a single coin” (Keohane & Nye 1987: 730). It is clear that a synthesis of DPT and Realism is possible when considering the multifaceted dimensions that create peace. Liberal ideology, realist concepts of power, and economic interdependence all play an important role in this.


This essay has argued that DPT provides a satisfactory explanation for the peace that exists between liberal democracies. The critics of DPT do succeed in finding some flaws in the theory, particularly with regard to the normative and institutional causal logics used, but these do not damage the core ideas of DPT, or the liberal ideology that underpins the theory. However, for DPT to be truly successful in explaining the peace between liberal democracies, a more balanced, holistic approach is necessary.

Alternative concepts such as Realism and economic interdependence must be brought in to fully explain democratic peace. Liberal ideology is just one factor that contributes towards the explanation of democratic peace. Concepts such as power and economic peace hold valid places alongside ideology. As this essay has shown, liberal ideology and economic interdependence are highly linked, and are most effective at creating peace when together. With Realism too, liberal ideology plays a role in shaping perceptions of state aggression, an important factor in creating liberal alliances. A synthesis between these three concepts will be the most successful in explaining democratic peace, as together they are capable of analysing all the factors which contribute to peace between liberal democracies. DPT therefore provides a satisfactory explanation for the peace that exists between liberal democracies. But for a truly persuasive explanation, DPT must also draw on the concepts of alternative theories.


BBC News. (2013). BBC News Europe. [Online]. [Accessed 11/11/2014]. Available from:

Dafoe, A. Oneal, J. Russett, B. (2013). The Democratic Peace: Weighing the Evidence and Cautious Inference. International Studies Quarterly. Vol. 57. pp 201-214.

Doyle, M. (1986). Liberalism and World Politics. American Political Science Review. Vol. 80. No. 4. pp .1151-1169.  

Doyle, M. (2005). Three Pillars of Liberal Peace. American Political Science Review. Vol. 99. No. 3. pp 463-466.

Gartzke, E. Weisiger, A. (2013). Permanent Friends? Dynamic Difference and the Democratic Peace. International Studies Quarterly. Vol. 57. pp 171-185.

Kant, I. (1795). Perpetual Peace: A Philosophical Essay. [Translated 1915].

Keohane, R. Nye, J. (1987). Power and Interdependence Revisited. International Organiztion. Vol. 41. No. 4. pp 725-753

Kinsella, D. (2005). No Rest for the Democratic Peace. The American Political Science Review. Vol. 99. No. 3. pp. 453-457.

Layne, C. (1994). Kant or Cant: The Myth of Democratic Peace. International Security. Vol. 19. No. 2. pp 5-49.

Levy, J. (1989). Domestic Politics and War. pp 79-100. In: Rotberg, R. Rabb, T. The Origin and Prevention of Major Wars. New York: Cambridge University Press.

Mearsheimer, J. (1990). Back to the Future: Instability in Europe after the Cold War. International Security. Vol. 15. No. 1. pp. 5-56

Mearsheimer, J. (2014). Why the Ukraine Crisis is the West’s Fault: The Liberal Delusions That Provoked Putin. [Online]. [Accessed 07/12/14]. Available from:

Mousseau, M. (2013). The Democratic Peace Unraveled: It’s the Economy. International Studies Quarterly. Vol. 57. pp. 186-197.

Owen, J. (1994). How Liberalism Produces Democratic Peace. International Security. Vol. 19. No. 2. pp 87-125.

Rosato, S. (2003). The Flawed Logic of Democratic Peace Theory. The American Political Science Review. Vol. 97. No. 4. pp 585-600.

Russett, B. Layne, C. Spiro, D. Doyle, M. (1995). Correspondance: The Democratic Peace. International Security. Vol. 19. No. 4. pp 164-184.

Small, M. Singer, D. (1982). Resort to Arms: International and Civil Wars, 1816-1980. California: Sage.

Walt, S. (1987). The Origins of Alliances. Ithaca: Cornell University Press.

Written by: Joseph Jegat
Written at: University of Leeds
Written for: Dr Adrian Gallagher
Date Written: November 2014

Please Consider Donating

Before you download your free e-book, please consider donating to support open access publishing.

E-IR is an independent non-profit publisher run by an all volunteer team. Your donations allow us to invest in new open access titles and pay our bandwidth bills to ensure we keep our existing titles free to view. Any amount, in any currency, is appreciated. Many thanks!

Donations are voluntary and not required to download the e-book - your link to download is below.