What causes marriages to crumble? Each couple is a little different of course, but are there specific work and financial pressures that seem to have a bigger effect on the soundness of any given union than another?

A spate of new research says there might be. It’s employment, specifically male employment.

One new study of 6,300 heterosexual couples found that all other factors being equal, men who were not working full time were 33% more likely to divorce in the following 12 months than husbands who did have full time jobs. “Contemporary husbands face higher risk of divorce when they do not fulfill the stereotypical breadwinner role, by being employed full-time,” said the author of the study, Alexandra Killewald, a sociology professor at Harvard University.

This is change in the last 40 years. For couples who were married before 1975, a husband who was not employed full time was less likely to divorce.

For years sociologists have argued over why couples split up and what policies should be put in place to try to coax couples into getting married or keeping them married. (This is not just meddling; an intact family is widely considered to be a sound unit on which to build a society, so governments have an incentive to try and keep them together.)

Financial pressures are often cited as one of the chief marital wrecking balls. Those with money can afford to outsource many of the more unpleasant chores of home life and have more time for bonding leisure activities and vacations. Those who have fewer resources, meanwhile, have more difficult lives and also have to deal with the stress that money worries put on a relationship.

But Killewald’s study, which will be out in the August issue of the American Sociological Review, disputes that suggestion: “My results suggest that, in general, financial factors do not determine whether couples stay together or separate,” she says.

Another theory for the uptick in divorce is that women have a lot more financial independence, with degrees and careers and wealth of their own, and thus do not feel dependent on their spouse or their marriage for financial stability. Two thirds of divorces are initiated by women, even though their chances of remarrying are slimmer than their ex-spouses’.

Nope, says Killewald. She compared marriages pre- and post-1975 and calculated, surprisingly, that women who divorced in the ’70s did not lose that much more income than women who divorced more recently. (She did this by comparing the income of similar women who were married and divorced, which is an imperfect measure, but probably as good as it gets.)

What made the difference was the role each spouse played in the marriage. Pre-1975 wives who did only did 50% the housework were more likely to get divorced than those who did 75%, but now, there’s no difference.

The effect of men’s unemployment was more stark. These days guys who have jobs have a predicted divorce probability in the next year of 2.5%, whereas the same guys who do not have a probability of 3.3%. That’s a third higher. This a big change from pre-1975, when the predicted divorce rate was slightly lower (1%) if they weren’t fully employed than if they were (1.1%).

Why are jobs so important to staying married for guys? Is it that women get mad at their spouses for not working and still not pitching in at home? Or is it that guys draw more of their identity from the work they do and they take out their frustrations in an inappropriate manner?

“It could be her, it could be him, it could be that unemployment is associated with other stuff like depression, it could be judgment from friends or family or lack of support for the marriage,” says Killewald. “These data just don’t tell me that.”

One thing is clear. It’s not because under-employed guys make less money; the figures didn’t change no matter how much they made. “When I show that husbands’ lack of full-time employment is associated with risk of divorce, that’s adjusted for income,” says Killewald. “It’s not how high earning he is.”

Killewald’s study buttresses recent work done by Johns Hopkins sociologist Andrew Cherlin, who found that pre-marital births were highest in the regions of the country in which income inequality was highest, which in turn were the areas with the most unemployment among high school graduates.

Cherlin has argued that couples will not marry—and signal that their union is official and permanent—until they believe they are on a stable financial footing or can see a path to a stable financial future. But they will not delay childbirth either. So without jobs or the prospect of jobs, couples end up not married and with kids. Again, marriage is linked to jobs. “I see those findings about the importance of men’s employment for getting married and staying married as absolutely part of the same cultural phenomenon,” says Killewald.

Another recent paper looked at whether government programs dissuade parents from getting married. Some couples lose benefits once their incomes are combined, so they opt to stay single. The paper from the American Enterprise Institute concluded that these programs do not seem to make a difference in the poorest families’ marital status, only among lower middle earners.

So what’s the fix, besides more jobs? One solution is to encourage a wider view of what a husband’s role in a family is. “We talk a lot about the changes in women’s experience, says Killewald, “but we haven’t done a lot of thinking about what it would be like for men to have a similar expansion in the ways they do masculinity.”

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