Although the decades between the passage of the Nineteenth Amendment to the United States Constitution (1920) and the 1960s are not included among the "wave" periods of feminism, this was a particularly important moment in the development of black feminist activism. During this period, a few radical black female activists joined the Communist party or focused on union activism. Although they did not all identify as feminists, their theorizing included important works that are the foundation for theories of intersectionality—integrating race, gender, and class. In 1940, for example, Esther V. Cooper (married name Esther Cooper Jackson) wrote a M.A. thesis called "The Negro Woman Domestic Worker in Relation to Trade Unionism". And in 1949, Claudia Jones wrote "An End to the Neglect of the Problems of the Negro Woman".