Were the Septims Nords?

Tiber was either a Nord or a Breton, depending on who you ask (I vote Nord), but he took an Imperial wife, as did his son. The Septim line actually had quite a few different races in it: mostly Imperials, but also a few Bretons, some Nords, a Redguard

here and there, even a dark elf (Katariah) at one point.

Were the Septims Nords or Imperials?

Tiber Septim/Talos was a Nord who founded the Empire, and yet by the time of the events in Morrowind/Oblivion the Septim dynasty is now Imperial, most evident by Uriel Septim VII and Martin Septim being coded into Oblivion as the race Imperial.

What race are the Septims?

Race. The exact race of Tiber Septim is unknown, but what is known is that he was not a Mer or Beastfolk, but a subspecies of Men. If the statement that he is from Alcaire is true, then he was most likely a Breton. According to Kier-jo, General Stormcrown was a Breton, not a Nord.