An "S" in Spain and "Z" in Americas

I apologize if this question has been asked, I did a search and could not find a substantive answer here. It is fairly common knowledge that Spanish names in the Americas have "Z" instead of "S". Chavez instead of Chaves. My rudimentary understanding is that the "Z" was used to deal with some of the indigenous sounds in words and names already in use in South America.

My question. Does anyone know when this change took place? Was there an official edict from Spain? Was it done after the revolution? I really would like to read about this subject. Any help would be appreciated.

Henry