When American women won the right to vote — a milestone commemorated on Women’s Equality Day, which marks the anniversary of the Aug. 26, 1920 certification that the 19th Amendment had been ratified — it was just one part of an even larger fight for equality. From Mary Church Terrell’s endeavors to make sure African-American women were included in the fight for suffrage, to Margaret Sanger’s work to promote access to birth control, to Ruth Bader Ginsburg’s efforts to eliminate sex discrimination in the law, women before and after that day in 1920 have fought for wider rights.

And yet, the U.S. Constitution does not say that people are equal regardless of their sex.

This fact came close to changing in 1972, when the U.S. legislature passed the Equal Rights Amendment (ERA), which stated that rights cannot be denied “on account of sex.” But after conservatives mobilized opposition to the ratification of the proposal, the amendment fell short of the three-quartersmajority needed to add the ERA to the Constitution. Now, as the Equal Rights Amendment has regained momentum — with two more states, Illinois and Nevada, recently ratifying it — advocates say that there’s a new opportunity for the ERA to move ahead.

Here’s what to know about Equal Rights Amendment history, what could happen to it next and how it could change American society.