Why was there a baby boom after World War II? A popular explanation is that the war postponed fertility, the men being away and the women busy with working. One could also argue that the Great Depression was a bad time to have children, and WWII prolonged that. Others argue that improved household technology made it possible to have more children.
Doepke, Hazan and Maoz argue that this was due to labor market competition after the end of the war. The war generated a huge demand for female labor, and those women continued to work thereafter. But those that were in school during the war faced stiff competition for jobs thereafter. Not having work experience, they were disadvantaged dropped from the labor market and had kids earlier. This is really a story of asymmetric response: the older women work more, the younger ones have more children.
But just stating this does not make it true. Doepke, Hazan and Maoz build an elaborate model of female labor supply and fertility decision, calibrate it for the period at hand, and are able to explain most of the dynamics seen in the data.