I got into a discussion with someone where I asserted that the idea of a Nation was relatively new in history, or at least in Western history. He insisted that nation states and national identities have long existed since ancient times. He specifically cited Rome as an example. Neither of us are experts, so I hoped this sub might offer it's expertise.
There was very much a sense of "Romanness" and Roman identity within the empire, and during the late republic and early empire there was an enormous amount of effort to create a shared history and common identity for the Roman people that bears a lot of similarity to nationalist projects of the nineteenth century (cf The Power of Images in the Age of Augustus). That being said, the Roman empire was in no way a "nation" nor did it ever pursue what might be deemed nationalist politics. The conquests, for example, were never justified under the rubric of irredentism or historical reclamation like, for example, the Nazi conquests of "Germanic" lands, nor was there really an attempt to enforce a normative "Romanness" over internal peoples like France did with Occitania.
The answer to this question is going to depend a lot on how you define "nation". Keep in mind that words change meanings (often quite drastically) over time, so while Latin does have a word "natio" related to our "nation", you shouldn't assume it means what you would mean.
So: what do you (and your friend) mean when you say that a place "counts as a nation"? What is it about national identity that makes it distinct from culture, race, ethnicity, language, etc? Without fully understanding the question it's very hard to give an answer.