So if I were trying to fit TES lore into it's best real world setting, we have to establish two things:
1. Tamriel is largely Indo-European in nature, seemingly encompassing the Alexandian/Roman Empires, although displays multiple anachronisms of different factions existing factions that were not chronologically contiguous.
2. There are hints of multiple cultures blended into each TES race, sometimes anachronistically. The Elder Scrolls is a fantasy series, after all. This means that no one cultural label will completely fit. That's how it should be.
With those settled, I surmised the following, attempting to keep each race at least somewhat centred in the Alexandrian/Roman Empires.
Men = European:
A. Imperials = Roman. This is easy to fit as their names, similar culture, and lore into the Roman Empire. Similarly, there seems to be a similar blending of Greek into this, as there is not really another culture to fit into the role of the Greeks so cleanly. Furthermore, Tiber Septim, while seemingly cast as Augustus Ceasar (the first Emperor of Rome) or Romulus (the quasi-mythological founder of the Kingdom of Rome) by Roman standards, fits better as Alexander the Great. Indomidable warrior and conqueror, yet a wise tactician and philosopher.
B. Nords = Germanic/Norse. Very old culture thriving in a harsh, frozen land. Known to define a person by their strength, believed in dragons, and made up a large part of the Late Roman Empire's military... Ironically, similar to the story of Skyrim, the fate and demise of the Roman Empire was greatly linked to the Germanics.
C. Redguard = Iberian/Spanish. Renown horseman and sailors. Only one culture of antiquity was so defined. Reguards also hail from Hammerfell, known for having a few ports along the coasts, and largely the rest of the land is arid/sandy desert. Spain, likewise, was known in the Roman age for the majority of the population being in maritime cities, while the rest of the Iberian Penisula was largely arid. The Moorish influence with Reguards also fits, as the southern part of Spain was Moorish, although this is a bit of an anachronism as the Moores were Islamic, which largely rose in the wake of the Roman Empire.
D. Breton = Celts. Because of the Forsworn in Skyrim and certain cultural/geographic similarities, Breton would seem to fit as the Celts. Though they lack the more primal ferocity of historical Celts, they do not lack in a territorial nature, strong ties to mystical arts and science, and frequent (almost tribal) in-fighting. They are also seen as having one of the oldest histories of the Men in Nirn.
Mer = African/Middle-Eastern:
A. Altmer (High Elves) = Pheonician. Stay with me here... Carthage was once the greatest threat Rome ever faced. Hannibal once marched an army through Spain into northern Italy, much like the Aldmeri Dominion marched through Hammerfell into Cyrodiil. Altmer have a culture mixing mysticism and philosophy, which also fits Carthage.
B. Bosmer (Wood Elves) = Parthian/Persian/Babylonian. A deeply religious and tyrannical culture where foreigners are disliked and strange rituals are performed. Also known for being some of the first cultures to implement spycraft as an art. Also known for some of the most feared archers before Alexander the Great.
C. Dunmer (Dark Elves) = Arabians. Originally known for being nomadic people surviving in a harsh environment who also had a significant (later deified) person in their history killed by means of betrayal. Once worshiping a pantheon of gods, this was later replaced with a far more strict religion. While some could draw parralisms between the Tirbunal of Morrowind and Islam, the religous persecution seen in The Elder Scrolls III more closely draws an anachronistic parrallel to the persecution of heretics (most notably Gnostics) during the Dark Ages in Europe.
D. Dwemer (Dwarves) = Ancient Egyptians. A culture long since dead by the time of the Roman Empire, the Ancient Egyptians still had a lasting impression on the history of Greeks and Romans alike. Known to be philosophical, industious, genius architects, and least mentioned, tyrannical. Known to employ a workforce of slave labour.
E. Falmer (Snow Elves) = Jews. A race without a home that was enslaved by the Dwemer (read: Egypt). Rebelled against Dwemer shortly before the Dwemer Incident. Known to be devout in the worship of one god (Auri-El versus the Abrahamic God). Where one was rendered blind by the malice of their opressors, the other was symbolically blinded for a long period when wandering through the desert.
F. Orismer (Orcs) = Sarmatians. What other culture would fit better than one that decreed that a virgin woman could not be married until she had killed at least three men on the battlefield?
A. Argonians = Indians. A very old culture that are seen as being a mystery to outsiders, largely due to a cultural xenophobia and geographical isolation. Known to live and thrive in a hostile swampy jungle that has monsoons that can kill. Known for some of the first court-appointed assassins.
B. Khajiit = Dacians. A particularly disliked race considered to personify an animal, and were histoically treated as outlaws. Dispersed around the entire Empire after their home was conquered. As such, they adapted nomadic traits, distrust of outsiders, and largely unknown cultural practices.
C. Akaviri = Far Eastern Oriental. With symbolism such as tigers, snakes, and dragons being placed next to the only known Akaviri-made weapons being Katanas/Wakazashis/Tantos, it is easy to see that this mysterious threat is a general amalgamy of Oriental cultures, predominantly featuring Chinese and Japanese.