The road which led me to RPGs began with my love of history. For me "history" fully included culture, religion, mythology, architecture, and many other related spheres of knowledge. Today, some 40 years later, I'm still a huge history buff even if nobody else in the family shares that passion (although my daughter finds bits of it interesting). So, when I start thinking about new game or campaign ideas I constantly feel the pull of history--it's like an intellectual form of gravity constantly drawing me back down to solid ground. This intellectual grounding is immensely helpful in building game worlds of my own and in making them feel more real during play. However it can also sometimes inhibit my creativity because certain concepts feel too "unrealistic".
A couple years ago when I started getting into the Pathfinder rules by Paizo, I immediately noticed the parallels between their Golarion game world and our own. I see the Golarion world as broadly similar in some ways to the Hyborian Age world used by Robert E. Howard for his Conan stories. And then I wondered how many people reading the Golarion world materials and perusing the maps would fail to notice those same parallels, given the often poor quality of education in many of America's schools and Americans' general lack of interest in history. Many parts of Golarion borrow shamelessly from world history and culture. The Lands of the Linnorm Kings up north is basically just a bunch of vikings, Galt is a direct port of the French Revolution, right down to the red, white, and blue color scheme and guillotine, and Osirion is pure ancient Egypt. There are a couple other examples, but you get the idea. Check out their Inner Sea World Guide and the Pathfinder wiki for details.
While I'm fine with games drawing on real-world history and culture, I was very disappointed with these direct "plagiarisms" by Paizo. I expected better of them. I have purchased quite a few of their Pathfinder/Golarion products and found them to be of high quality. In particular, I enjoy their Adventure Paths. Clearly, Paizo has a lot of talented creative people working for them. So why the cheap, cut-and-paste jobs?