Every cuisine has a foundation of ingredients. In Mexico, it was squash, corn, and beans. Each region then added their specialties to this foundation. In the Yucatan Peninsula, seafood was the primary addition along with fruit-based sauces. In northern Mexico, the meat was almost always grilled over an open charcoal fire. Oaxaca is thought to be the place corn was first domesticated. Even today, there are many varieties of corn grown in this area that can be found nowhere else. Chiles are another staple in this area. They make seven different varieties of mole sauce in Oaxaca.
The Origins of Authentic Mexican Recipes
Every country has its own food, and that food usually comes together from a number of different places. I liked this little article that talks a bit about the origins of authentic Mexican recipes: