During the Merovingian and Carolingian times in early medieval Europe, it is interesting to note that having an extended family was a matter of survival for ordinary people. One needed to depend on the family for physical backup in case any trouble, such as accusation of adultery etc, occured. Ordinary folks slept as large families of around 8-12 people in large thatched buildings.
Until recently – prior to the industrial revolution – it appears that an extended family continued to be a matter of survival for most societies. In India, for example, extended families were the norm until a few decades ago. With the industrial revolution, the state became more empowered and thus law was able to be better enforced. Protection could be provided to smaller units such as the nuclear family.