When I was younger I saw it as:
Davion: Western Europe, what was left of the North American space colonies, and a smattering of other groups.
Steiner: Pan-European, with small numbers of other groups.
Marik: All groups, including the ones you never thought of.
Liao: China, Russia, Southern Asia, and the British Isles minus England.
Kurita: Japan, Russia, Scandinavia, the Middle East, and Latin America.
These days I see it more as: Everybody has every group, but the proportion changes from state to state. You can find Swedes in the FWL, but most of them will be found in Rasalhague. Africans live in the Commonwealth, but more of them live in the Combine, and so on.
I think part of it comes from the continuing evolution of the game's backstory, and the Combine is especially targeted by this. I'll argue no state, even the Capellans or the Taurians has undergone more changes in the overall tone or depiction of their society in the past 30 years than the DC.
Mechwarrior 1st ed./Sorenson's Sabers: The Combine is a dictatorship. The family that rules it is of Japanese heritage, some of the people associated with it have Japanese names. Other than this, very little of the state has any Japanese flavoring in its institutions. To the point that the word samurai is almost never mentioned, and one duel is described as being fought with epees instead of Japanese swords. In many ways this version of the Combine has more in common with the Empire from Star Wars than it does with later depictions from just a few years later.
House Kurita SB/Gray Death Trilogy: The books that formed the basis of the Combine as most of us view it. Japanese people form a minority, but an influential one both politically and culturally. "Orientals" (the term used throughout these books) form a very large part of the population, maybe a slim majority.
The Combine is a dystopian mix of Stalin's Soviet Union, Imperial Japan in the 30's and 40's, and any number of family-run dictatorships common in the mid to late 20th century. Non-Oriental people are oppressed, but the degree to which they are oppressed run a gamut of complex social factors and stellar geography (general rule, the more peripheral you are to House Kurita's rule, the less flak you take in your personal habits unless you get ratted out to the ISF). Guys with last names like Clay, Hamid, and Samsonov can become powerful noblemen and generals, but they need to follow the Combine's version of bushido and political orthodoxy to do so. Rasalhague does not fall into line with this, so they get pushed around even harder than the other peons, but House Kurita will make small compromises with non-Japanese groups in order to keep greater stability in their empire.
Robert Charrette's Combine can be considered an evolution of this above Combine, with some of the more over-the-top brutality and cartoon villainy removed. Charrette showed that the average Combine citizen has some good in his heart, and there are some truly outstanding people who live and die under the banner of the Dragon, even if they pay a high price for it. Overall however it is still a pretty grim place to live, Theodore's reforms offering a ray of hope that things might get better.
Stackpole's novels: Where do I begin? Stackpole does a decent job of expanding much of the Japanese warrior ethos from earlier books, but he distorts it as well for dramatic purposes. He also depicts the Japanese as being a much larger share of the population than many of the earlier books, which is either good or bad depending on your personal tastes. There are few shades of grey to be found here, either the Combine is the worst thing ever or another one of the white hats, depending on the needs of the greater story. Generally he depicts it as softening under Theodore to the point where it seems not much worse than its neighbors, and much better than the Clans it opposes.
Milan's novels: A mix of the above versions with some original concepts thrown in. Milan's Combine plays up the blending of various cultures; there are different and distinct ethnic blocks, but at the edges they have merged with other groups from centuries of autocratic rule under House Kurita. Jeffery Kusonoki is the poster boy for this: He is blond, blue-eyed, two-meters tall, has some degree of Asian ancestry but above all considers himself a samurai dedicated to seeing House Kurita conquer the universe and crush all inferior cultures.
Eastern and Western concepts have been mixed together into a syncretic mix that is recognizable to the reader, but gives Combine culture a distinct bent from "Japan as seen by America" that existed in earlier works. The activities of the social classes outside of the military get more focus. The Combine is a police state, but one where the business of everyday living needs to be done as well.
Personally, this is one of my favorite depiction of the realm, and really makes it come alive.
Modern books (From 2005 to now): A mix of the old sourcebook, Stackpole, and Milan thrown together. Generally even darker and more cynical in its depiction of the Combine than earlier sources, as part of a general trend in the material produced for the entire game universe.