In my last segment, I argued that the Long Peace is really a composite of four relationships, and that the most important of these — Cold War stability — is either the result of factors that will not persist, or results from the ideological nature of the contest in ways that have yet to be carefully analyzed. Perhaps because of the complexity and possible irrelevance of the Cold War, attention has increasingly shifted to the liberal peace as a guide to the future.
The observation that developed democracies seldom fight each other is arguably the most important discovery in the recent study of international relations. Yet, before we credit democracy with peace, we must consider the possibility that whatever causes democracy is itself responsible for the relative absence of conflict among liberal states. Unfortunately, researchers have yet to agree on a canonical explanation for democracy, making it difficult to determine whether the causes of democracy might themselves be the causes of peace. What I outline below is thus speculative, only partly backed by evidence and by logic.
As I noted in the last segment, peace requires that no nation perceive a benefit from acting aggressively. It is tempting to believe that democracy could accomplish this. Yet, while western liberal democracies are certainly “nice” to each other, there are several reasons to wonder whether this is due to democracy, per se. We already know that democracies are not more peaceful monadically. In addition, Mousseau shows that only rich democracies benefit from democratic peace. If democratic peace only works among satisfied states, then perhaps it is these states’ circumstances, rather than their politics, that leads these nations to cooperate. My own work suggests that countries with similar interests are much less likely to fight, independent of regime type. This may explain the effect of democratic peace by itself, though this claim is disputed by others. In a forthcoming paper, I also show that the strength of the democratic peace seems to be declining as the number and diversity of democracies grows. Researchers have begun to distinguish between “good” (i.e. liberal) and “bad” democracies (Zakaria). It will come as no surprise to readers if democracy in the Middle East and North Africa produces regimes that are not Western friends. Finally, the democratic peace has proven surprisingly resistant to coherent explanation. As Charles Lipson quips “We know it works in practice. Now we have to see if it works in theory!
There remains something intuitive about the claim that democracy and peace are related. Yet, this may be because democracy comes from peace, rather than producing it. Indeed, democracy alone among domestic political systems requires peace as a prerequisite. As soon as the loser in an election takes up arms to reassert political success, democracy is in jeopardy. Domestically, democracy requires that political losers prefer defeat to the use of force. The same must be true internationally of course in order to maintain stability.
A compatibility of interests helps to account for democracy within and the lack of conflict between polities. A society in which the population lacks a critical consensus about policies is unlikely to form or survive as a democracy. Tensions between policy preferences should tend to either prevent democratization or destroy it, as political losers cannot accept defeat on peaceful terms. This is the story of Weimar Germany and indeed of the U.S. Civil War. If, in addition, democracy tends to form domestically only when populations are centrist in their preferences, then the “median” or “pivotal” actor in these centrist democracies will tend to be more similar than the pivotal preferences among autocracies (given the effect of majoritarian rule). Democracy will be associated with moderate foreign policies, not because democracy causes moderation, but because moderation causes democracy.
At the same time, nations fight over more than just policy differences. Tangible material goods can also form the basis for conflict. Here, it is economic development that appears to play a crucial role. In published and unpublished research, I have shown that developed states are much less likely to fight over territory (though no less prone to dispute policy differences). The rising cost of labor associated with economic development has meant that most modern nations prefer to buy the fruits of territory rather than seek to conquer (steal) land directly. Economic development also just happens to be the most widely used and accepted predictor of domestic political liberalization. Prosperous, which just happen to cluster geographically, are both much less prone to fight over where their borders ought to be and much more likely to be democratic. The increasing productivity of labor and the inefficiency of coercion make it much more appealing to govern societies through consent, rather than through coercion. Conquest, and tyranny, no longer pay. This implies that development leads both to a decline in territorial conquest and to a rise in democracy.
Growth in the number of democracies in the world may provide enough impetus to sustain and even broaden the Long Peace, if the causes of peace lie largely in political liberalization. Systemic liberal peace advocates have suggested exactly this relationship. However, stable democracy has been slow to materialize in many regions; the shift to majoritarian rule has not coincided with the consolidation of liberal norms or institutions often thought to be the key factors in promoting liberal international peace. Similarly, there is some evidence that the democratic peace is not as robust after the Cold War. If instead development causes a shift away from territorial aggression, then there is reason for hope in the very processes that appear to be leading to a multipolar world. China, India, and other developing nations may join the West in eventually eschewing conquest as a viable foreign policy option.
Where tensions will remain is in the area of the nature and content of global and regional governance. Ironically, as the world becomes more integrated, the stakes in having one’s way in the world have become much higher. Without unipolarity, the world’s leading nations must find new ways to compromise and dissect differences, rather than allowing them to accumulate into indigestible omnibus disputes. Though the work on international institutions shows relatively little pacific effect, their greatest impact may be yet to come.
Erik Gartzke is an associate professor of political science at UC San Diego. Gartzke’s primary area of study involves the impact of information and institutions on war and peace. He applies bargaining theory, rational choice institutional theory, concepts of power and social identity, and statistical analysis to four substantive areas of interest: 1) The liberal peace, 2) international institutions, 3) diplomacy, and 4) the system overall.
 It would by no means be a large exaggeration to say that half of Political Science seeks to explain democracy, while the other half is using democracy to explain other things.