On Sunday, the world celebrated International Women’s Day to commemorate the social, economic, and political achievements of women. In the United States, such celebrations turned attention to the Equal Rights Amendment (ERA), a proposed amendment to the constitution that would guarantee “equal rights under the law” to all Americans regardless of sex.

The amendment was first proposed nearly 100 years ago, not long after passage of the 19th Amendment which gave women the right to vote.

The ERA, written by Alice Paul and Crystal Eastman, came in response to what many feminists at the time regarded as limitations that persisted despite the 19th Amendment. Feminist groups, including the National Woman’s Party, had campaigned for specific issues, but the ERA was regarded as a comprehensive constitutional amendment.

Opponents of the ERA – including some women’s reform groups – argued that the amendment would damage existing laws that protected women against exploitation.

Congress did not pass the amendment until 1972. States were given seven years to ratify the amendment. But, by that time, only 30 of the required 38 states had ratified the ERA. The deadline was extended to 1982, but by then some states had rescinded their earlier support.

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The matter lay largely dormant in Congress for years, with some activists accepting defeat, and others acknowledging that women had obtained many of the rights that the ERA was designed to provide.

In 1997, Supreme Court Justice Ruth Bader Ginsburg said there was “no practical difference between what has evolved and the ERA,” but qualified that she would still like to see the ERA in the Constitution as a “symbol” for her granddaughter.

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But, in recent years, the ERA has seen renewed enthusiasm. This past January, Virginia became the 38th state to ratify the amendment. And, last month, the House passed a bill that would remove the deadline for ratification of the ERA. Since then, it’s remained in the Republican-controlled Senate awaiting approval.

Still, Ginsburg said last month she’d prefer that the process “start over” from the beginning.