Simone de Beauvoir wrote a detailed analysis of women's oppression in her 1949 treatise The Second Sex. It became a foundational tract of contemporary feminism.[66] In the late 1960s and early 1970s, feminist movements, such as the one in the United States substantially changed the condition of women in the Western world. One trigger for the revolution was the development of the birth control pill in 1960, which gave women access to easy and reliable contraception in order to conduct family planning.