Also. Let's be fair here. One of the reasons we know so much about the Romans and Greeks for example is because they, as a group of people, held record keeping in some esteem and as a result. We know the difference between say Macedon and Sparta because their records, military organization and cultures have some variation in them. Certian people after the fall of Rome had enough reverence for their culture and as a result kept as many records as they could about what made Rome a superpower. Unfortunately many other cultures did not write down as many records if any at all. Even still the ones that did write a comprehensive amount of things down don't usually get the same amount of reverence from their conquerors and many of those records were lost to looting. I would like to point out as well that much of what we know about the Celts, early Germans, Scythians, ect come to use from Greek, Roman, Persian and to a lesser extent early Norse historians/writers as well as archeological evidence. Many European cultures of the time wrote very little themselves. Most had no form of written word and imported their written language from others. This is why those distinctions exist is because they are attested and referred to by multiple sources. There are many if not more African tribes as well. There's just not as many records that help differentiate them for historians to go through. As a result things get muddled.