There’s an assumption about women in power that you may have heard: that women who lead tend to be more diplomatic than their male counterparts, resulting in a more peaceful world. Psychologist Steven Pinker, for instance, wrote in his 2011 book, The Better Angels of Our Nature, “Over the long sweep of history, women have been and will be a pacifying force.” But how much of that is true?

After sifting through historical data on queenly reigns across six centuries, two political scientists have found that it’s more complicated than that. In a recent working paper, New York University scholars Oeindrila Dube and S.P. Harish analyzed 28 European queenly reigns from 1480 to 1913 and found a 27 percent increase in wars when a queen was in power, as compared to the reign of a king. “People have this preconceived idea that states that are led by women engage in less conflict,” Dube told Pacific Standard, but her analysis of the data on European queens suggests another story.

Interestingly, Dube and Harish think the reason why queens were able to take part in more military policy can be explained by the division of labor that tended to happen when a queen — particularly a married queen — ruled. Queens managed foreign policy and war policies, which were often important to bring in cash, while their husbands managed the state (think taxes, crime, judicial issues, etc.). As the authors theorize, “greater division of labor under queenly reigns could have enabled queens to pursue more aggressive war policies.” Kings, on the other hand, didn’t tend to engage in division of labor like ruling queens — or, more specifically, they may have shared military and state duties with some close adviser, but not with the queen. And, Dube and Harish argue, it may be this “asymmetry in how queens relied on male spouses and kings relied on female spouses [that] strengthened the relative capacity of queenly reigns, facilitating their greater participation in warfare.”

Here’s Dube and Harish with more on that:

Female reigns may have had higher capacity to carry out war since queens often put their spouses in charge of official state matters. This division of labor would then have freed up time and resources for queens to pursue more aggressive war policies. In contrast, kings typically were less inclined to put their spouses in official positions through which they could aid in managing the polity. This asymmetry in spousal division of labor emerged in several realms. Since women didn’t serve as heads of militaries, queens would often appoint their husbands to this role, though kings of course, did not do the same with their wives.. As an example, when Queen Dona Maria II of Portugal married Prince Augustus Francis Anthony in 1836, their marriage contract stated that he would serve as commander in chief of the army.

And when husbands of queens managed state affairs, the success of the country was strong. The authors point to Francis Stephen, who revamped the Austrian economic system while his wife, Queen Maria Theresa, used that cash to bolster the army. “Spousal support,” in other words, was a win-win for these royal couples, allowing queens to not only be more invested but also more successful than their peers who acted alone. (Modern couples, take note.) That doesn’t mean that queens and kings always agreed — qualitative data suggests that, in fact, queens and kings often disagreed, and virulently, with some queens marching onto the battlefield without their spouse’s approval. And a few kings weren’t too happy with being “king-consort,” bickering with their wives over the title.

The queens’ marital status made a difference here; as the authors write, “among married monarchs, queens were more likely to participate as attackers than kings.” If a queen were single — which was the case with 13 of those they studied — she was more likely to be attacked compared to the times when a king was in power, perhaps because her country was seen in the outside world as being more vulnerable and thus easier to attack.

But the authors emphasize that the increase in wars on a queen’s watch is not likely explained by an attempt by the female leaders to signal their strength. Were that true, you’d expect a spike in war participation earlier in the queens’ careers, and that wasn’t the case according to the data analyzed here. Dube and Harish also argue that the queens were not actively seeking to fight more wars. But here are a few more relevant commonalities of queenly reigns: Queens didn’t tend to use war ministers as much as kings, they relegated other tasks to their husbands, and they often threw themselves into the policy-making machine wholeheartedly.

It’s just a working paper, which means that Dube and Harish may uncover more as they continue to research this subject. But so far their findings have already begun to poke a few holes in some commonly held assumptions.