“Equality of rights under the law shall not be denied or abridged by the United States or by any State on account of sex.” For nearly a century, those 24 words have been the subject of a longstanding battle to win women equal protection under the law. The proposed amendment is simple, but the fight to add the Equal Rights Amendment (ERA) to the U.S. Constitution has been anything but.

The amendment has its roots in the aftermath of the suffrage movement. Some activists were ready to retire after the 19th Amendment was finally passed in 1920, but Alice Paul was determined to keep fighting for the entirety of the women’s rights program laid out by founding suffragists in 1848. “We always had perfect loyalty to the whole program and, if we could continue, we knew that the thing must extend to get the whole program a reality,” she said in a 1972 oral history.

View Images Activist Alice Paul pushed for the Equal Rights Amendment after the 19th Amendment secured voting rights for American women. Photograph by Harris & Ewing, Library of Congress

In 1923, Paul announced plans to develop and champion a constitutional amendment guaranteeing equal protection to both sexes. She named it after women’s rights pioneer Lucretia Mott. It was introduced in the 68th Congress in December of that year by Representative Daniel Read Anthony, Jr. and later revised and renamed after Paul.

The concept hit roadblocks from the start. Many came from other women’s rights activists, who feared the amendment might endanger hard-fought laws that protected women workers. Those concerns, and split opinions on women’s rights, haunted the amendment for nearly 50 years.

The ERA was introduced in Congress over and over again, but despite tantalizing victories, like public hearings and its passage in the Senate in 1946, it was never adopted. Meanwhile, the women’s rights movement changed dramatically as old-guard suffragists passed the torch to new activists. Paul continued her tireless advocacy for decades. She finally found the support she needed in the late 1960s, when second-wave feminists helped push it toward passage. Finally, in 1972, the ERA passed both chambers of Congress. (Here's how women around the world are taking charge of their futures.)

The hard work wasn’t over yet. To be added to the Constitution, three-quarters of the states had to ratify it within the seven-year deadline attached by Congress. But though it enjoyed broad popular support and was even part of both the Democratic National Convention and the Republican National Convention’s national platforms from the 1940s on, the ERA fell victim to political shifts.

Backlash to the women’s movement and the increasing conservatism of the Republican Party gave fuel to Phyllis Schlafly, an activist who opposed feminism and the amendment. Though legislators extended the deadline to 1982, the savvy opposition of Schlafly and her allies slowed and even stopped progress in several states. The Republican Party removed the ERA from its platform, and five states voted to rescind their ratifications in the 1970s. The amendment missed its 1982 deadline only three states shy of ratification.

But is the amendment really dead? Maybe not. Nevada and Illinois ratified it in 2017 and 2018, leaving it just one state shy of the majority—until Virginia’s General Assembly passed the ERA in January 2020.

Given that the seven-year ratification deadline has passed, though, it could face significant legal hurdles even with another ratification. Supreme Court precedent states that amendments must be ratified in a “contemporaneous” timeframe. On the other hand, the 27th Amendment, which prohibits Congress from handing itself a bump in pay before an election, was suggested and written by James Madison more than two centuries before its ratification in 1992. And it’s not clear how the states that rescinded their ratifications would be handled even if Congress agrees to accept the latecomers. (Essay: Why it's time for women to demand equality.)

Though a constitutional amendment could never address all disparities, the amendment’s supporters say it could provide clearer definitions of gender discrimination and prevent a rollback of women’s rights to things like abortion. Despite recent successes, however, the ERA’s future is still uncertain—and the most contentious phase of its century-long history could still lie ahead.