Which Might and Magic universe are you referring to?

A question for those who understand Ashan. Regarding the styling.

Haven — European culture
Sylvan — Slavic culture
Sanctuary — Buddhist culture
Academy — Islamic culture
Fortress — Scandinavian culture
Stronghold — ? (Mongolian (5) or Aztec (6) culture)
Dungeon — ?
Necropolis — ? (Egyptian (6) culture)
Inferno — ?

Could someone clearly correlate these? Which culture does each faction ultimately adhere to?

It is not that simple.

Based on official information, the sources of inspiration are (quoting):

Haven:

- Medieval Western Europe (general atmosphere and setting);
- Roman Empire (militarized structure and the principle of ”Pax Romana”);
- The Order of Templars (the sense of a sacred mission);
- Victorian England (puritanical morals and strict social stratification).

Inferno:

- Greek Maenads / Bacchantes (mad followers of Dionysus-Bacchus);
- Rome during the period of decline (Nero, Caligula, Heliogabalus);
- Carthaginian and Aztec priests.

Necropolis:

- Ancient Egypt (Book of the Dead);
- Buddhism (asceticism and rejection of the physical world due to its illusory and fleeting nature);
- Various sects (fanaticism, cult of personality, strict order, and spiritual purity).

Sanctuary:

- Zen Buddhism;
- Eastern martial arts;
- Samurai of the Sengoku Jidai era;
- Shaolin monks;
- Yogis and spirits from Indian mythology.

Stronghold:

- Pre-Columbian South American tribes (Aztecs, Mayans, etc.);
- Polynesian tribes (Maori);
- African tribes (Maasai, Zulu).

Official information about the sources of inspiration for the other factions will likely appear as they are released in Heroes 6.

Added after 1 hour 26 minutes
I will add a bit of my own:

Haven - for the most part, yes, Medieval Europe. Moreover, each duchy corresponds to a specific region of it.

Duchy of the Griffin - Eastern Europe, where Russian names predominate (Nikolai, Alexei, and Andrey from Heroes 5; Anastasia, Anton, Kirill, Irina, Slava, Svetlana from Heroes 6) as well as Hungarian (Sandor, Istvan).

Duchy of the Ox - Italy (Ornella, Orlando, Giovanni) and possibly Spain and Portugal.

Duchy of the Wolf - Germany (Gerhard, Mark, Karl, Martina).

Duchy of the Hound - most likely France (Isabelle, Elizabeth, Beatrice), but not for certain.

Duchy of the Stag - Ireland and Scotland (Duncan, Kieran, Deirdre).

Duchy of the Unicorn - ancient Scandinavia (Godric, Frida) and again Ireland and Scotland (Fiona, Aidan).

Duchy of the Falcon - England and again Ireland and Scotland (Liam, Ronan, Maeve, Brian, Brendan).

Duchy of the Raven - unidentified, as I do not know any representative of this duchy and likely won't in the near future, because this duchy only appears after the fall of the Falcon Empire.

Inferno - overall, it can be attributed to ancient Greece and Rome. In any case, judging by the architectural style of their castle in Heroes 5.

Necropolis - official sources are somehow silent about the Sumerian notes in Heroes 6. Take, for instance, the Sumerian ziggurat. Does it remind you of anything? Or the fact that Lamassu is a guardian spirit in Sumerian-Akkadian mythology.

Sanctuary - as was previously mentioned, it is mainly a mix of Japan, India, China, and Thailand. There is plenty of obvious evidence for this. However, this mix is slightly seasoned with Greek style in the image of the coral priestesses (i.e., medusas) in typical Greek draped garments.

Stronghold - the situation here is very interesting. In Ashan, there are 3 types of orcs: Mongolian (Heroes 5), Aztec (Heroes 6), and Arabic (have not appeared yet). Moreover, the Aztecs are heavily seasoned with influences from other wild peoples. For example, the orc capital on the Pao islands is called Taumata-Kunyaq. Taumata is a locality in New Zealand.

Sylvan - the elves have plenty of nods to Celtic culture (druids with Stonehenge, fairies, unicorns and, of course, the elves themselves), as well as to Native American culture. For example, feathers, face paint, long double braids. Remember the hairstyle of the elf Ossir, and compare it with the hairstyle of a Native American. To be honest, I don't see anything from the Slavs in the elves at all.

Academy - as already mentioned, they are clearly Arabs with a mix of India.

Fortress - indisputably Scandinavians.

Dungeon - the hardest faction to identify. Some find the Italian Renaissance in it. But, IMHO, no single people correspond to this faction. Inspiration during its creation was most likely drawn from the dark elves of the Forgotten Realms world (R. Salvatore's novels).

In general, I once thought that Ashan followed the principle of 1 faction = 1 real people. But now I realize that Ubisoft mixed too many things here. For instance, India is present in both the nagas and the mages. And Celts are found among the elves and slightly among the humans.