When people are asked to name a historical point that D&D most closely represents, they'll usually say something like "The Middle Ages", or perhaps a date between 1000 AD and 1500 in Europe. Truth be told, to find a historical period which has a social setup anything like D&D, you're going to have to go back. Way back. D&D represents a period in history that is most closely identifiable with the Iron Age: the landscape is dotted with tribes and aspiring empires, the wilderness is largely unexplored, and powerful individuals and small groups can take over an area without having a big geopolitical hubbub about it.