As the U.S. Congress begins debating whether to authorize President Barack Obama to strike Syria for using chemical weapons on its own people, a new study challenges the conventional by claiming that the propensity for modern nations to go to war is as strong as it ever was.

The idea that countries are less likely to engage in war with each other today than in the past has been argued by a number of academics in recent years, including Harvard University psychologist Steven Pinker, author of the 2011 book The Better Angels of Our Nature: Why Violence Has Declined.

The new study, presented last week by Ohio State University professor Bear Braumoeller at the annual meeting of the American Political Science Association, challenges that idea, finding that states are no less violent today than they have been through history.

Since the end of World War II, the world has not experienced a war between great powers. But this 70-year lull, often called “the Long Peace,” has hardly lacked intense global conflict.

The trend has led prominent observers, with Pinker in the vanguard, to argue that both societies and states—in particular democracies tasked with maintaining international norms—are becoming less violent over time.

In The Better Angels of Our Nature, the gradual fall in interstate conflict is one part of what Pinker sees as a global trend at all levels, with a downtick in violence extending from small social groups to entire countries.

Violence is on the decline “at many scales—in the family, in the neighborhood, between tribes and other armed factions, and among major nations and states,” Pinker writes. “To my repeated astonishment, the global trends in almost all of them, viewed from the vantage point of the present, point downward.”

And even though that earlier 40 million dead may appear a huge number, as a percentage of the overall population it may represent a decline in war deaths from previous centuries, according to Pinker.

Debate Over Measuring War Propensity

But are states actually becoming more peaceable, or are they merely constrained by diminishing opportunities to wage war? That was the question Braumoeller was trying to get at in his study.

“My goal,” he said, “was to try to control for the opportunity of states to fight one another so that we could get a clear picture of their willingness to fight, and see if this willingness has increased or decreased.”

Braumoeller challenges Pinker’s claim that the best statistical measure of a state’s propensity toward violence is war deaths per capita. In his book, Pinker utilizes war deaths per capita primarily because it allows for levels of violence to be compared across millennial time scales and because it takes into account the relative size of states.

As societies organized themselves into more cohesive state structures, Pinker argues, the per capita war death rate steadily fell, with the decline accelerating over the last century.

A billion people lived on the planet in 1800, compared to three billion in 1960, and seven billion today. The per capita war death rate has declined with population growth, from 70 per 100,000 people in 19th century France, to 60 during the first half of the 20th century (including from two world wars), and to three-tenths of a person per 100,000 today.

But Braumoeller notes that exploding human population growth over the last two centuries ensured that war deaths simply could not keep up with the expansion rate. While wars have steadily increased in casualties, particularly during the large-scale conflicts of the early 20th century, the casualty counts lagged considerably in comparison to total population.

“Almost any state-level phenomenon, divided by population, is going to decrease over time,” Braumoeller said, “because population increases dramatically.”

Fewer Chances to Fight?

So Braumoeller proposes a different gauge for how prone a state is to war: measuring how often it engages in conflict.

Using the Correlates of War Militarized Interstate Dispute database—a compilation of conflicts in which one or more states threatened, displayed, or used force against one or more other states between 1816 and 2012—Braumoeller found that while instances of conflict experienced peaks and troughs throughout history, the total number held largely steady from the end of the 18th century up until World War.

Following World War I, that number began to grow, but largely because of the explosion of newly independent former colonies.

“The opportunity for countries to fight has changed quite dramatically over the course of the past two centuries,” said Braumoeller. “As empires have broken apart, and as new countries have been created, on average countries are getting smaller, weaker, and further apart.”

And these small, weak states have much less geographic opportunity and political reason to engage in war.

While the United States, with its globe-spanning military capabilities, may choose to intervene when its Middle Eastern interests are threatened by a civil war in Syria, very few other countries have that sort of geopolitical reach.

Take Uruguay. Realistically, it can only go to war with Argentina or Brazil since its modest military, minimal economic clout, and geographic location make it unlikely even to invade Paraguay anytime soon, much less Iran.

Put differently, war is predicated on a state having the opportunity, might, and impetus to make war. A large country, with many neighbors, global interests, and opportunities for grievance, will have more chances and reasons to engage in war.

When controlling for these variables—geographic opportunity and political relevance—Braumoeller finds that states are just as likely to act aggressively.

“I found that the willingness of states to fight one another really doesn’t change very much at all,” he said. “It’s gone up in some periods and down in others, in a sort of cyclical trend. We see warlike periods—19th century, early 20th century, and the cold war—but there is no clear trend in one direction or another.”

All Military Interventions Created Equal?

Pinker, responding to questions via email, took issue with many of Braumoeller’s arguments. He said that measuring all instances of conflict, without distinguishing between major wars and minor skirmishes, conflates “trivial shots across the bow” with wars that kill significant numbers of people.

While Braumoeller refers to each instance as a “roll of the dice” with the potential to escalate into a larger war, Pinker argues that all interventions are not the same: there is far less escalation risk in firing cruise missiles into Sudan, as the U.S. did in 1998, than in invading Iraq, as the U.S. did in 2003.

Pinker also says that Braumoeller fails to take into account the conscious choice by many states over the last half century to conscientiously degrade their ability to make war—by cutting back on conscription and war expenditures as a percentage of GDP. If countries were just as likely to go to war as they use to, they would have no incentive to undertake such reductions.

While neither theory claims to be predictive when it comes to individual cases, to Pinker the recent debate over whether to attack Syria may point to a restraining effect international and humanitarian norms have had in reducing conflict.