Short answer for this question please
During World War II, somebody had to go into the factories to build the guns, tanks and other heavy equipment used by the American men overseas. It was the American women who assumed this seemingly masculine task of welding, constructing, etc. When the men returned home, a second income was recognized as a progressive asset. Many men encouraged their women to remain active in the labor market.
Furthermore, immediately after World War II, the famous BABY BOOM occurred. This was an explosion in the baby population as these men came home and had children with their wives.