The accepted conservative notion of what constitutes a typical American nuclear family has been two biological parents and their offspring. For many families, the typical family unit would also include the grandparents since families tended to live together as a matter of necessity and convention.
The Gold Rush transformed traditional families by making grandparents part of the extended family when Easterners moved towards the West to seek their fortunes. This image of family persisted all through the 1970's.
In reality, the nuclear family has always had variations to the theme due to abandonment, divorce, death and reconfiguration of household members that included remarriage. The 1950's stigma of divorce did nothing to curve its rates, but may have had a great deal with encouraging second marriages to maintain propriety and ensure children from a previous marriage had a male figure in their life as well as financial support, while perpetuating the widely accepted role of women as homemakers.
With the end of the Great Depression and World War II, the 1940's saw the greatest increase in marriages and a sharp increase in family size that continued all through the 1960’s. The offspring of this generation are what we refer to today as the "baby boomers." Families from this era commonly had an average of 3 to 4 children.
In the1960's and 1970's, women shed their identity as the primary caregiver and gave themselves permission to pursue their passions in higher education and in careers previously held by males. With the subsequent opportunities obtained through higher education, women were able to postpone marriage and child bearing as well as deciding whether to have children or not. The wide distribution and availability of birth control, coupled with the consistent message from the women's movement that women could be more and do more widely resonated with a new generation of women, and allowed men the freedom to be more than just breadwinners.
The baby boomers flourished as independent thinkers that restructured conventional acceptance about the composition and meaning of what constitutes a traditional family. They also changed the financial landscape of the country and gave rise to a consumer society that was in sharp contrast with the conservative spending habits of their parents and grandparents. This economic boom and excessive materialism influenced the composition of the nuclear family once again.