Among professional and merchant elites, the married couple replaced the large extended family as the core unit of the household. The shift showed up first among the groups whose work and wealth were tied to new careers and trade.
Once the husband-wife bond became the ideal family, women could use the terms of that ideal to claim new rights for themselves. An ideal that seemed to bind women to the home also gave them words to make demands.
Arguments about who a community or nation is were fought out through arguments about how families should be arranged. Changing the household meant taking a side on larger questions of belonging.
A family can be understood mainly as a unit that holds and passes on property, or mainly as a bond of affection between its members. Which view prevails shapes who counts as family and what each member can claim.