While there is evidence of nuclear families existing as far as 5 000 years ago, they were only really for wealthy/high status people. The concept of the nuclear family as it’s own autonomous unit wasn’t really widely financially viable until post-Industrial revolution.
There is even current academic arguments that the previously believed idea that Europe had moved to nuclear families as early as the 17th century may be flawed, as the surviving literature was once again biased towards the merchant/upper classes.