What was the baby boom?
Some historians have argued that it was a part of a desire for a normalcy after 16 years of depression and War. Others have argued that it was part of a Cold War campaign to fight communism by outnumbering communists. Most likely, however, the post-war baby boom happened for more quotidian reasons. Older Americans, who had postponed marriage and childbirth during the Great Depression and World War II, were joined in the nation's maternity wards by young adults who were eager to start families. (In 1940, the average American woman got married when she was almost 22 years old; in 1956, the average age American woman got married when she was just 20. And just 8 percent of married women in the 1940s opted not to have children, compared to 15 percent in the 1930s.)
So your answer would be:
•The tremendous increase in population following the war.
