About nine years ago, Hakuo Yanagisawa, the former health minister of Japan, blamed his country's shrinking population on the finite number of women - or, as he called them, "birth-giving machines."

"All we can do is ask them to do their best per head," he asserted in a gaffe heard around the world, reinforcing gender stereotypes that still gripped Japan: Men earned money, while women belonged at home.

Recent data, however, reflects a startling shift: Japanese women now outpace American women in participation in the labor force. Sixty-four percent of working-age women in Japan are employed, compared with 63 percent of American women.

The Japanese employment rate surged in recent years as the rate in the United States declined and then stagnated. The numbers may confuse casual observers, especially those who recall Yanagisawa publicly defining women by their fertility in the not-so-distant past. And for generations, American women led the developed world in female employment. So, what happened?

Economists don't know for sure. The culprit could be a combination of changing attitudes toward mothers at work in Japan and relatively limited support for mothers at work in the United States.

In 2013, Japanese Prime Minister Shinzo Abe announced that he would prioritize gender equality in the workplace, calling it vital to sustained economic growth. Among his goals: to raise the share of mothers who return to work after the birth of their first child to 55 percent by the year 2020, which he believes would boost the country's gross domestic product by 15 percent. A 1999 report from Kathy Matsui, Goldman Sachs's first female partner in Japan, fueled the idea, dubbed Womenomics.

"Japan is a country with a shrinking population caused by a seemingly intractable decline in its birthrate," Abe wrote in a 2013 Wall Street Journal op-ed. "But Womenomics offers a solution with its core tenet that a country that hires and promotes more women grows economically, and no less important, demographically as well."

Meanwhile, the recovery in the United States has been painfully slow, especially for women.

Roughly 8.7 million jobs vanished during the most recent recession. Since the downturn ended, however, men have encountered less trouble getting back to work, according to the Economic Policy Institute. Between February 2010 and June 2014, men gained 5.5 million jobs, while women gained 3.6 million.

Economist Heidi Hartmann, president of the Institute for Women's Policy Research, blames this on a blend of forces: The United States doesn't offer family-friendly workplace policies, such as paid family leave or sick days, and the gender wage gap hasn't budged much in a decade.

"The question is, why didn't we continue to make upward progress?" Hartmann said. "That's partly because women don't feel like they get a fair break in the labor market."

One thing Japanese women have that many American workers lack is financial help for new mothers. They receive 58 weeks of maternity leave, 26 of which are paid. Fathers are entitled to the same amount of time off, though less than 2 percent actually take it.

Abe has also pledged to create 400,000 day-care spaces nationwide by 2018. Parents also receive a "child allowance" from the government, implemented and recently doubled to "reduce the economic burden" on families.

Parents in the United States receive no such benefits unless their employers supply it. An estimated 43 million American workers, mostly those at the bottom of the pay scale, report having no access to paid leave. Economists say that's one reason the United States has been trailing other countries in the quest for a work-life balance. A growing body of research shows that mothers, far more than fathers, are forced to scale back at work or quit, even if they need the income.

In 1990, the women's labor force participation rate, for ages 25 to 54, was 74 percent, the sixth-highest among 22 of the world's most advanced economies. By 2010, as other countries adopted and expanded family-friendly workplace policies, American women slid to 17th place - "a stunning reversal," wrote Cornell University researchers Francine Blau and Lawrence Kahn.

"Such policies likely facilitate the labor force entry of less career-oriented women," the authors concluded. "On the other hand, entitlements to long, paid parental leaves . . . may encourage women who would have otherwise had a stronger labor force commitment to take part-time jobs or lower-level positions."

Blau and Kahn argued that there was a mixed outcome: Women in countries with these government mandates could more easily stay in the workforce, but some met discrimination from employers that barred them from promotions. For example, a young woman in a job interview might hear, "Do you expect to have children soon?"

No one policy fix can vanquish unconscious biases that affect hiring decisions, experts say. But talking about the importance of attracting and retaining female workers across all levels, as Japan's Abe does, could encourage progress, Hartmann said.

There's incentive for governments worldwide to back that mission: "Getting more women to work outside the home does grow GDP," she said.

In the 1970s, for example, when more women and a surge of baby-boomer men entered the workforce, 65 percent of growth arose from workforce expansion, according to a McKinsey Global Institute report. Today, the study suggests, nearly 80 percent of growth comes from productivity increases - and American women still disproportionately remain on the economic sidelines.