The making of of a sauce by combining chiles, tomatoes and other ingredients like squash seeds and even beans has been documented back to the Aztec culture..
We have Spanish-born Bernadino de Sahagun to thank for the detailed culinary history of the Aztec culture. His extensive writings documented every food common to the culture. This is an excerpt from Sahagun's writings about the food vendors in the large Aztec markets:
"He sells foods, sauces, hot sauces, fried [food], olla-cooked, juices, sauces of juices, shredded [food] with chile, with squash seeds, with tomatoes, with smoke chile, with hot chile, with yellow chile, with mild red chile sauce, yellow chile sauce, sauce of smoked chile, heated sauce, he sells toasted beans, cooked beans, mushroom sauce, sauce of small squash, sauce of large tomatoes, sauce of ordinary tomatoes, sauce of various kinds of sour herbs, avocado sauce. (Sahagun, translated 1950 -1982).
Ingredients Then and Now The paragraph above refers to many of the ingredients in our modern-day salsas.
Large tomatoes - We believe this references is to a large red tomato similar to what we eat to day.
Ordinary tomatoes - most likely this reference is to the tomatillo or tomate verde.
Smoked chiles - The chipotle or smoked jalapeno was a staple in the Aztec diet.
Avocado - cultivated by the Aztecs the avocado was an important source of fat and protein and was used in a sauce similar to what we call guacamole.
Salsa in American Cookbooks The Encyclopedia of American Food & Drink reports that the 1st mention of the term "salsa" appeared in print in the U.S. in **1962. Further, they mentioned that as of 1991 the sales of salsa surpassed that of our U.S. staple, ketchup.
**Our research has documented recipes for salsa were printed in a U.S. cookbook published in 1898. The book was Encaracion Pinedo's El Cocerina Espanol (The Spanish Cook). She included a recipe for "Salsa Picante de Chile Colorado" a spicy red chile sauce as well as "Salsa de Chile Verde" a green chile sauce. Both salsas were fresh, uncooked salsas.