In 1908, on the last Sunday in February, socialist women in the United States initiated the first Women's Day when large demonstrations took place calling for the vote and the political and economic rights of women. The following year, 2,000 people attended a Women's Day rally in Manhattan.

　　In 1910 Women's Day was taken up by socialists and feminists throughout the country. Later that year delegates went to the second International Conference of Socialist Women in Copenhagen with the intention of proposing that Women's Day become an international event. The notion of international solidarity between the exploited workers of the world had long been established as a socialist principle, though largely an unrealised one. The idea of women organising politically as women was much more controversial within the socialist movement. At that time, however, the German Socialist Party had a strong influence on the international socialist movement and that party had many advocates for the rights of women, , including leaders such as Clara Zetkin.

　　Inspired by the actions of US women workers and their socialist sisters, Clara Zetkin ;had already framed a proposal to put to the conference of socialist women that women throughout the world should focus on a particular day each year to press for their demands. The conference of over 100 women from 17 countries, representing unions, socialist parties, working women's clubs, and including the first three women elected to the Finnish parliament, greeted Zetkin's suggestion with unanimous approval and International Women's Day was the result.

　　That conference also reasserted the importance of women's right to vote, dissociated itself from voting systems based on property rights and called for universal suffrage - the right to vote for all adult women and men The voice of dissent on this decision came from the English group led by Mrs. Despard of the Women's Freedom League, a group actively engaged in the suffragette movement.

　　Conference also called for maternity benefits which, despite an intervention by Alexandra Kollontai on behalf of unmarried mothers, were to be for married women only. It also decided to oppose night work as being detrimental to the health of most working women, though Swedish and Danish working women who were present asserted that night work was essential to their livelihood.