The decline in death rates, which has meant an overall increase in the world population, gave rise to the birth control movement. Scientific advances during the eighteenth and nineteenth centuries resulted in better food supplies, the control of diseases, and safer work environments for those living in developed countries. These improvements combined with progress in medicine to save and prolong human lives. During the 1800s, the birth rate, which in earlier times had been offset by the death rate, became a concern to many who worried that population growth would outstrip the planet’s ability to provide adequate resources to sustain life.

In 1798 British economist and sociologist Thomas Robert Malthus (1766–1834) published his Essay on the Principle of Population, arguing that populations tend to increase faster than do food supplies. He thereby concluded that poverty and suffering are unavoidable. Malthus viewed only war, famine, disease, and “moral restraint” as checks on population growth. In spite of or because of Malthus’s assertions, during the 1800s the idea of birth control as a practical method to keep population growth in check gained momentum.

Early in the 1900s the movement found a leader in American Margaret Higgins Sanger (1883–1966), whose personal experience as a nurse working among the poor had convinced her that limiting family size is necessary for social progress. She became convinced that unwanted pregnancy should be avoided by using birth control methods. It was—and remains—controversial. Even though the distribution of birth control information was illegal at the time, Sanger advised people on the subject. In 1914 she founded a magazine called The Woman Rebel, and she sent birth control information through the mail. She was arrested and indicted. But she was not deterred. In 1916 in Brooklyn, New York, Sanger founded the first birth control clinic in the United States. In 1921 she organized the first American Birth Control Conference, held in New York. That same year she founded the American Birth Control League, which later became the Planned Parenthood Federation of America. As public support for the movement increased, Sanger succeeded in getting laws passed that allowed doctors to disseminate birth control information to their patients.

In other countries, Sanger’s work inspired similar movements, but developed nations continue to have lower birth rates than do developing nations. With the world population exceeding 5.5 billion, the fear of overpopulation had prompted new interest in birth control.