As she threw open the doors to 46 Amboy Street in Brooklyn’s Brownsville neighborhood on the morning of October 16, 1916, 37-year-old Margaret Sanger must have known she would be arrested again. In 1914, she had been indicted for sending her newsletter, The Woman Rebel, through federal mail—an act prohibited by a piece of legislation passed in 1873 and named after anti-vice crusader Anthony Comstock. Although Sanger avoided jail by fleeing to England for a year in 1915, her husband William was arrested and served time for handing out a pamphlet on “family limitation” to a police agent in New York City.

And this is how Sanger and her feminist allies took their first momentous stand for reproductive health in the United States. Almost a hundred years ago today, on October 16, 1916, in an immigrant neighborhood, they opened the first clinic in the United States that would offer contraceptive advice and supplies. Astonishingly, given Sanger’s prominence in New York socialist circles, it took nine days for an arrest warrant to be executed. The charges? Not distributing birth control, or “rubber goods” as they were known at the time, but rather “giving information regarding birth control.” On November 13, just as she had warned the judge at her bail hearing she would, Sanger reopened the clinic. Although the police had confiscated many of her medical supplies, she assured the reporter following her case that “she would get along as well as she could without these.”

The most important element (and weapon) of Sanger’s fight for women’s right to birth control, and the one that put her in violation of federal law, was her use of speech. So-called “barrier methods” made from rubber, including condoms and cervical caps (sometimes known by a nineteenth century euphemism, the “womb veil”), were already a staple of the twentieth century middle-class woman’s birth control arsenal. But advertising, discussing, or furnishing educational materials to women regarding these methods was considered obscene under the Comstock law. Too many women knew little about their own bodies or about how conception occurred, much less about how sex could actually be pleasurable for them rather than a burden. As a socialist, Sanger believed that sex education was critical, not just for preventing childbirth for women who would have little access to medical care, but also for lifting working families out of poverty, something that was intensified by the economic toll of unwanted children.

Sanger had intimate knowledge of the challenges poor families faced. A trained nurse and the mother of three sons, she grew up in a working class community. She was born to Irish immigrant parents on September 14, 1879 in industrial Corning, New York, and was the middle child in a family of eleven. She may never have known her mother when she wasn’t pregnant, grieving a miscarriage, or nursing an infant. By the time she opened her clinic, Sanger had, however—thanks to both her education and her marriage—joined the ranks of the middle class. Nonetheless, her past allowed her to more fully grasp the hypocrisy of the obscenity laws that equated necessary information about human reproduction with pornography. Such laws helped limit access to what she called “birth control” methods to only those middle class women who could afford the right doctors. In 1911, as they became increasingly drawn into political circles, the Sangers moved to Manhattan. Margaret became a visiting nurse on the Lower East Side, where she began to increasingly view pregnancy as an important cause of illness, poverty and malnutrition.

Believing that information was the best weapon, Sanger began to write about sex in frank, readable prose. From 1911 to 1912 she published a series of articles in The New York Call entitled “What Every Mother Should Know; or, How Six Little Children Were Taught the Truth,” which urged parents to scuttle fairy tales about where babies came from and speak honestly to their children about sex. A second series, “What Every Girl Should Know,” (1913) explained the facts of sex and human desire, including masturbation.

In 1914, she began to circulate these collections as pamphlets in the United States mails, knowing that she risked arrest for doing so. But sexual ignorance, she believed, was part of a larger public health crisis. “Students of vice,” she observed, had, so far, failed to stem the tide of venereal disease and unwanted children by suppressing information, a view that was shared by many feminists – and even some of Anthony Comstock’s allies in the social purity movement. The need for education had “shown itself so clearly,” Sanger wrote, “that the question no longer seems to be, `Is there need of instruction?’ but `Who shall instruct?’”

The clinic on Amboy street was one answer to that question, the first determined shot in a battle that would crack open the door to legalizing birth control over the next half century. Sanger became a beacon of the movement, but also a symbol of its ongoing entanglement with eugenics in the United States. Some popular advocates of eugenics, such a Theodore Roosevelt, opposed birth control because it would give white women the option to reduce childbearing. Sanger, on the other hand, worked frequently among immigrant women and argued that birth control could instead help reduce births among the ethnic groups that eugenicists viewed as “unfit.” As the United States entered World War I in 1917, Sanger wrote of birth control’s “social and racial value.” By 1920, in Women and the New Race, Sanger blamed the war itself on the pressure of German overpopulation, warning that armed conflict “kills off, not the weak and helpless, but the strong and the fit.”

Yet Sanger’s record on race is as complicated as the history of birth control itself, and her attachment to larger political issues may have been opportunistic rather than ideological. As a combination of poverty and Jim Crow segregation meant the denial of health care to more and more African-American women, she worked with leaders like W.E.B. DuBois to expand sex education and proven birth control methods in Black communities, opening Harlem’s first neighborhood clinic in 1930. Later generations of activists viewed Sanger’s efforts in the negative light of her alliance with eugenics, but it is also the case that Planned Parenthood, which evolved out of Sanger’s American Birth Control League, remains, today, a leading health care provider for women— and men—of color in the United States.

Sanger would live to see the battle for women’s right to control their own bodies shift away from its focus on free speech and toward one aimed at the right to privacy. In 1965, the year before Sanger’s death, Connecticut’s director of Planned Parenthood, Estelle Griswold, was vindicated in her Supreme Court challenge to a state-level Comstock law. Establishing the right to marital privacy, Griswold v. Connecticut voided bans on birth control nationwide, paved the way for the decriminalization of abortion in Roe v. Wade, and was cited in Court decisions that led to the legalization of same-sex marriage.

Sanger likely did know, when she ushered her first clients into the waiting room a century ago, that she would be arrested. But she was probably unaware of how influential this first, bold step would be, the extent to which her aspirations for female reproductive health would come true, how soon women would be able to speak frankly about sex, and that the war against those who would censor free speech about birth control would be successful.

Indeed, as feminists fight to preserve a century of progress, reproductive choice continues to hinge on the free distribution of information that allows women to take control of conception, defend their right to pleasure, and resist the stigma of refusing motherhood. Nowhere is the right to speech more important than in resisting the conservative attacks on abortion that seek to punish women for having sex at all. As Cecile Richards, director of the organization that Sanger launched a hundred years today, noted in 2014: “It’s important that women be able to share their stories and experiences openly if they choose to, so that they can connect with each other and begin to end myths and misconceptions about both the procedure and the women who have it.”

As Sanger welcomed her clients into the clinic’s comfortable waiting room, she may have been having this exact thought.