The most basic decisions in creating a D&D character are the selection of race and class. To these parameters I would propose adding a third dimension, culture. The purpose of the cultural parameter is to sort through a large array of chargen options to create patterns in the campaign world. Examples:
Culture one (bog standard fantasy)
races: human, half-elf, hill dwarf, high elf, halfing, gnome
classes: fighter, cleric, wizard, rogue
prestige classes: arcane archer, eldritch knight
Culture two (the vaguely Norman guys invading the island home of culture one)
races: human, half-elf, grey elf, mountain dwarf, gnome, half-orc, orc
classes: warmain, paladin, cloistered cleric, magister, unfettered, mageblade
prestige classes: assassin, tactical soldier, archmage
weapons: bastard sword
Culture three (Celtic? Norse? Whatever.)
races: human, half-elf, wood elf, deep dwarf, troll
classes: barbarian, ranger, spirit shaman, scout
Culture four (Orientalist adventures, ahoy!)
races: human, mountain dwarf, wood elf, goblin, hobgoblin
classes: samurai, shujenka, sohei, wu jen, ninja, monk
prestige classes: contemplative, ronin, dragon samurai, kensai, ghost-faced killa
Members of each culture would speak a cultural tongue in addition to Common. Characters would only have access to classes, prestige classes, feats, etc. from their own culture. To add something from another culture I envision some kind of mechanic hurdle has to be jumped. Maybe a feat 'Worldly', with a pre-req of speaking one or two other cultural languages.
I would also make some classes non-culture specific. I'm thinking here about the NPC classes, the Generic classes from Unearthed Arcana, and maybe self-taught classes like Sorcerer. World-spanning organizations might have prestige classes outside the culture system as well.
An additional benefit is that a clever DM can filter out particularly annoying class/race/whatever combos. Hate spiked chain fighters? Put spiked chain in one culture and the fighter class in another. Make the players work to achieve the most tasty cheese.
Explosive Ordnance Disposal
2 hours ago