Remember that the Mexican food phenomenon took place in the 1960s, mainly because of the rise in migrant workers who had come into the United States. Before that time, Mexican food, much like Chinese food, was limited to the ghettos and ethnic neighborhoods of major cities or farming communities. Without large numbers of Chicano/Latino families to introduce the food to the public, even along the border areas, Mexican food would have been considered relatively exotic....Mexican food would still be prevalent throughout the Southwest. Isolationism or no isolationism, the economy of the region--especially in the agricultural sector--is largely dependent upon a steady flow of inexpensive labor from Mexico. You'd have to have a very good reason to keep that from happening, and in a manner that doesn't cause food to become prohibitively expensive.