Your example is probably correlation, not causation. Median incomes in the US stagnated at the same time as more women entered the workforce, but that does not mean that the latter caused the former.<p>Stagnating or declining middle-class incomes in the US is probably caused by (1) exporting manufacturing jobs to Asia, and (2) weakening organized labor. It may also be caused by (3) deregulation which increases the share of income going to capital and decreases the share going to labor.<p>If you look at the experience in Canada during the same time, median incomes grew faster than in the US, even though Canada was also adding women to the workforce. This is probably because Canada did not weaken organized labor as much as the US did.