What caused the 1943-1964 baby boom?

Prior to the Baby Boom, there was a period of approximately 20 years in which having children would have been difficult due to the Great Depression and World War II. The Baby Boom reflected the sudden removal of economic and social pressures that kept people from starting families.[3] While austerity and restraint were the norms during the stress of the war years, after the war, couples reunited and returned to traditional roles. Returning (mostly male) soldiers re-entered the workforce; many women left wartime work to concentrate on child-bearing and child-rearing. Marriage became again a cultural and career norm for most women - and one result was babies. The boom continued in the economic glow of the fifties, but dampened its rate as the recession of 1958 sloughed into the following recovery. One theory about the end of the baby boom is that it petered out as the biological capacity of boomer parents took its course. The key biological factor is female fertility. Women are fertile only into their mid-forties. Simple mathematics governs that a woman married in her mid-to-late twenties after the war ended in 1945 would remain fertile for another 20 years or so. The advent of the birth control pill in 1960 in the U.S. also contributed to the slowing birth rate, as earlier contraceptive methods were less popular or reliable.