Comment by Inthenameofmine

For most people in most societies it always was. It just used to be surplus value extraction from the wife for the husband and clan, and later the capitalist employing the husband. With the increase in bargaining power of women in society extraction of surplus value bacame more two-way and the capitalist class was able to extract surplus value directly from the women instead of roundabout through the men. Hence both partners need to work to have the same living standard as before with just one partner working.