I think I'd need quite a lot of evidence that families weren't the major unit of society. A hunter-gatherer tribe is an extended family, so that only proves the point. If there's more than about 30 people in one then surely family based factions will form within it to some extent.

Probably you're focusing too much on the parent comment's mention of nuclear family. Even that, despite only being named a few decades ago, is likely to exist to some extent. Even in some ancient tribe or village, most people would favour their spouse (or equivalent) or child over a cousin or niece/nephew if some dispute formed. That hardly seems controversial.