The National American Woman Suffrage Association (NAWSA) was an organization formed on February 18, 1890, to advocate in favor of women's suffrage in the United States. It was created by the merger of two existing organizations, the National Woman Suffrage Association (NWSA) and the American Woman Suffrage Association (AWSA). Its membership, which was about seven thousand at the time it was formed, eventually increased to two million, making it the largest voluntary organization in the nation. It played a pivotal role in the passing of the Nineteenth Amendment to the United States Constitution, which in 1920 guaranteed women's right to vote.