Immanuel Kant proposed that countries ruled by the people would be reluctant to go to war, except in cases of self-defense, because the people know that they would be the ones who might die on the battlefield. Kant, continued, arguing that if all countries were ruled by the people, a "perpetual peace" would emerge and persist.
Later, Thomas Paine argued that autocratic countries would be more likely to go to war because kings feared that their legacies and pride were at stake. In countries ruled by the people, the people would prevent rulers from taking rash, violent action. This, Paine said, was Common Sense.
These ideas came to be called democratic peace theory and were assumed true for more than a century, before being put under the microscope by scientists in the 1960s.
In the first scientific study of democratic peace theory, Dean Babst calculated the probability that any two countries would declare war against each other. Then, he compared whether the countries he deemed democratic (places where citizens have choices between opposing parties and can vote at regular intervals for members of a legislature and executive branch) were less likely to go to war than non-democratic countries. He found that the overall probability of any two randomly selected countries would go to war was 8%. When looking only at the democratic countries and their historic declarations of war, he found ZERO pairs of democratic countries declaring war on each other. In other words, in this data set, there was 0% probability of democratic countries declaring war on each other.
This research provided evidence suggesting that democracy may cause peace. As with all research, though, there are a number of issues with this single study.
One of the biggest issues is that most of research on democratic peace theory relies on correlational historical reports. Correlation cannot demonstrate causation. It may be that democracy is not actually causing peace, but rather some other variables that tend to co-occur with democracy. For example, democracies tend to have higher gross domestic products per capita and stronger militaries. So, maybe rich countries are less violent. Or, maybe countries build strong militaries to deter others from wanting to fight with them.
Another issue with this research is that all of the data are at the nation-level and do not look at the psychology of the decision-makers who choose to enter conflicts (or not).
At the Summer Institute in Political Psychology, Stanford University Professor Michael Tomz reported findings from two experiments designed to get around the problems of the past studies of democratic peace theory that relied on the aggregated correlational data. In these studies, participants read short descriptions of different countries with key factors like gross domestic product, military strength, and how leaders gain power (elected or not) systematically varied so that they could look at how each of those variables uniquely affect their participants' perceptions. After reading about these countries, participants indicated their support for using military action against each of the countries. In support of democratic peace theory, people were less likely to attack the countries described as democratic, regardless of the country's other characteristics.
But, these data do not tell us the psychological mechanisms why people in democracies are less likely to support conflicts with other democracies. Thus, Tomz conducted another study in which he assessed people's perceptions of other fictitious countries that might be relevant in deciding to go to war with them. Specifically, he asked participants:
- How threatening is the opponent?
- How costly would an armed conflict with the opponent be?
- What is the likelihood of success?
- Would it be moral to attack them?
Not surprisingly, people support war against threatening countries. And when war is expected to be less costly. And when there is a high probability of success. And, when war against a specific opponent would be moral.
Importantly, though, these perceptions eliminated the effect of democracy on support for peace. Specifically, people presume democratic countries to have more similar morals, be less threatening, and less likely to be successfully defeated. When examined individually, perceptions of threat and morality were most important in understanding the relationship between democracy and peace.
Radical dovish liberals may point to recent military endeavors led by the United States and its coalition of the willing and disagree with this assertion. If they can set aside their motivated reasoning, to reject information inconsistent with their desired conclusions (like, the idea that America is a war-mongering nation responsible for countless atrocities abroad and deserving of any horrible terror attacks it receives), they may see how democracies are typically less violent than their autocratic counterparts.
On the other hand, radical hawkish conservatives may take this evidence that democracies are more peaceful as a justification for going to war with autocratic regimes, thinking that will make those countries more peaceful in the future. Supporters of going to war with Iraq often made this argument. While the evidence seems to suggest democratic countries are less likely to go to war, trying to force a democracy upon a country may not be sufficient for it to really embrace democratic ideals.
In sum, democracy may not directly cause peace, but it can reduce how threatening people feel other countries are and how moral a war against other countries would be. There's still much research to be done on democratic peace theory, but the ever-improving methodological techniques used in the examination of it leads to increased confidence that democracy leads to a reduction in international conflict.