From the Washington Free Press:
Women are a revolutionary force. That fact shows in their holiday, International Women's Day (IWD), both its past and present.
The holiday's roots are in the struggles of working women and their socialist supporters. It's believed that a mass protest by women garment and textile workers in New York City in 1857 occurred on March 8, and that in March two years later the same women won a drive to unionize. They were fighting against brutal working conditions, low wages, and the 12-hour day.
On March 8, 1908, socialist women organized a demonstration of 15,000 in New York. Their demands were pay raises, shorter hours, the vote, and an end to child labor. After that, the Socialist Party of America decided to celebrate a women's day in the US, the first of which was held in 1909.