According to a 2012 paper titled “Men Rule: The Continued Under-Representation of Women in U.S. Politics” by Jennifer Lawless of American University and Richard Fox of Loyola Marymount University, the biggest factor is that fewer women run for office. A lot fewer. The two academics list seven reasons why:

* Women are more likely than men to see the electoral environment as highly competitive and biased against female candidates.
* Hillary Clinton’s and Sarah Palin’s candidacies aggravated women’s perceptions of gender bias in elections.
* Women are less likely than men to think they are qualified.
* Potential female candidates are less competitive, less confident, and more risk averse.
* Women react more negatively than men to many aspects of modern campaigns.
* Women are less likely than men to receive the suggestion to run for office.
* Women still handle the majority of childcare and household tasks (no surprise there!).

Yet, the two say in their summary, “Study after study find that, when women run for office, they perform just as well as their male counterparts. No differences emerge in women and men’s fundraising receipts, vote totals, or electoral success.”

Another factor often cited is sexist media coverage of female candidates. A nonpartisan group called “Name It. Change It.,” a joint project of the Women’s Media Center and a group called She Should Run, released two studies in 2013 reporting on media’s focus of women candidates’ appearance and the use of sexist language in covering campaigns. Female candidates lost ground when media used terms like “ice queen” and “mean girl” in describing candidates, and also lost ground when media focused on a candidate’s appearance, whether those descriptions were positive or negative. When female candidates insisted that coverage and campaigns focus on issues instead of appearances or name calling, the candidates regained ground.

But it’s a tall order. Every time Hillary Clinton changes her hairstyle, it’s covered as news and is interpreted as sending a message about her presidential intentions. How much has been written about her black pantsuits? How much about Sarah Palin’s clothes?

Of course, the tactic can backfire. In 2014, a Republican state lawmaker called Rep. Annie Kuster “ugly as sin” and predicted that the Democratic incumbent would lose to her “truly attractive” opponent, Marilinda Garcia. That was even too much for New Hampshire voters; Kuster won.

The first woman to serve in Congress was Rep. Jeanette Rankin, a Republican from Montana who was elected to the House in 1916. She was one of 50 legislators to vote against joining World War I, which killed her House re-election chances in 1918 (she ran for the Senate as a third-party candidate and lost). She was elected to Congress again in 1940, when she became the only member of Congress to vote against declaring war on Japan. “As a woman I can’t go to war, and I refuse to send anyone else,” she said of that vote.

Rankin had worked successfully to give Montana women the right to vote in 1914, so it was no surprise that she worked hard to pass the 19th Amendment in Congress during her first term in Congress, guaranteeing women the right to vote nationwide. “How shall we answer the challenge, gentlemen?” she asked her male colleagues “How shall we explain to them the meaning of democracy if the same Congress that voted to make the world safe for democracy refuses to give this small measure of democracy to the women of our country?”

The first African-American female senator was Sen. Carol Moseley Braun, a Democrat from Illinois who was elected in 1992. Rep. Shirley Chisholm, a Democrat from New York, was the first African-American woman to serve in the House. Rep. Patsy Takemoto Mink became the first female Asian/Pacific Islander to serve in the House; the Hawaii Democrat was first elected in 1968.

Sen. Mazie Hirono became the first female Asian/Pacific Islander to serve in the Senate; she was elected from Hawaii in 2012. Rep. Ileana Ros-Lehtinen became the first Latina to serve in Congress; the Florida Republican has served two separate districts and was first elected in 1988. There has never been a Latina in the Senate.

What about the top positions? Nancy Pelosi became the first-ever House Speaker in 2007, and she’s still House minority leader. But when it comes to leading a country, that’s a glass ceiling the U.S. has yet to crack. There have been female leaders on six continents (seven if you count female penguins leaving the males at home to tend the eggs), but not in the U.S.

There have been female presidents, prime ministers, and governor-generals in Western and non-Western countries: Argentina, Australia, Brazil, Canada, Chile, Germany, Great Britain, India, Ireland, Israel, Nicaragua, Pakistan, South Korea — and many more. A woman, Soong Ching-ling, was even the acting co-chairperson of China.

March is Women’s History Month, and March 8 is International Women’s Day. The next national election day is not until Nov. 8, 2016. It’s likely there could be a woman at the head of the Democratic Party’s ticket in Hillary Clinton. Might it be too much to hope for that there would be more women on the ballot in other races, too?