Most women entered in the labor force for the first time during WWII. In the US, for instance, many job positions were empty when the war started as, after the draft, many men were forced to join the armed forces and went to the battlefronts either the Europe, to the Pacific theatre of to the North African one.
As production levels had to be maintained for the well-functioning of the country, women occupied such empty positions and kept production processes working. This was the first contact with the labor force for many of them, and it meant a turning point as, along the second half of the 20th century, female employment figures grew spetacularly.