Well, these social groupings have been important well into the twentieth century. In the middle of the century, a leader arose in a particularly warlike central European tribe who combined millinarianism with mystified teachings regarding tribal identify bolstered by a fabricated lineage. Eventually a coalition of surrounding tribes were able to beat them back, and this lead to them establishing a supra-tribal council to mediate disputes.

So I'm assuming you are wise to my game here, my point being that "tribe" and "clan" is not a well defined or solid category. This is not to say that forms of social organization peculiar to this or that culture, bit the designation of "tribe" generally has less to do with any scientific categorisation than with a generation desire to establish distinction between "civilized" and "uncivilized".

This really delves into anthropology, and people like /u/khosikulu and /u/firedrops can handle it better.