How did the Italians use to preserve their dry meats like Mortadella or Prosciutto? before nitrates and nitrites were used?

Salt is used to dry the meat and low moisture means low organism growth also the smoked meats had chemicals from the smoke which did the same. They discovered some sources of salt kept the meat red (and this was found out due to nitrites in the salts). Nitrites also stop botulism organisms from growing. Also, if you notice many cured and fremented products have a sourness or a tang to them. That is due to acids (lactic acid or acetic acid (vinegar). Low pH retards organism growth also.