If women worked it generally wasn't out of economic necessity because they needed two incomes to survive.
What changed?
Why do we now need two incomes?
It seems to me wages began a long period of stagnation in the 70s' and the cost of living has increased faster than wages.
What were the economic/social shifts?
The U.S. was the only industrial power to emerge from World War II with its infrastructure and industrial capacity unscathed. We were able to enjoy a very high standard of living because nobody else could compete with us in most industries.
There is this misconception among a lot of people that these were the "good old days," and we could just go back to that if we wanted to. The reality is that those years were an anomaly in history, not the norm.
By the 1970s, Europe and Japan were back on their feet and new emerging countries like South Korea, Taiwan, Malaysia and Indonesia were starting to become major global competitors.
In my family, grandmas would often provide free childcare in case the mother had to work. My dad’s mom had to work, and her mother lived with them and raised the kids.
We now know that the post WW2 period and the twenty five years that followed were an aberration—prosperity based on one income and strong family values by women.
The combination of gigantic multinational corporations (who loved cheap labor) and the “progressives” social policy that dominated the mass media, education, non-profits were a toxic mix.
The cost of housing in many areas of the country, has increased far beyond the rate of inflation and income growth innrecent decades. This has undoubtedly caused many young families to look at their finances, and conclude that mom should work so they can afford a house.