Unlike the English and French, who wanted to rule their subjects and keep their distance, Spanish imperialists plunged into the midst of their new found land, destroying what they could and embracing what they couldn't.
Then, Spanish was the language of one country on southern Europe. Now it has become the primary tongue for 20 countries and, by the end of the century, an estimated 400 million people.
The King and Queen of Spain, two Nobel laureates and hundreds of experts assembled in Zacatecas in Mexico this week for the First International Conference of the Spanish Language. If there was one conclusion reached on the first day, it was that Spanish has a bright future.
"We Spanish and Hispano-Americans are the owners and users of one of the four great languages of the near future, the others being English, Arabic and Chinese," said 1989 Nobel laureate Camilo Jose Cela of Spain.
The conquistadors created throughout Latin America something they called "criollismo": an indigenous society, shot through with ethnic and linguistic variations from Tierra del Fuego to the Rio Grande, that, despite vast divergences spoke a common tongue, Spanish, or as they prefer it, Castillian.
The tag "Latin" (instead of "Hispanic") America was apparently imposed by the French after the Archduke Maximilian's ill-fated attempt to rule Mexico in 1860s.
Yet by then it was too late. The huge wealth of gold and silver had mostly been dug up, shipped out and squandered, creating in the process a vibrant Spanish-speaking culture that produced more Nobel literature prize-winners than the mother country.
"We slept with many women but we married them too," was how one Spaniard summed up a process that differed fundamentally from the British in India and the French in Africa.
Shaw's dictum that Britain and the US were divided by a common language could never be applied to relations between Spain and Latin America. They understand each other all right, and acknowledge the bonds between them.
But with the duration and depth of Spanish penetration, words survive in Latin American parlance that went out of use in Spain centuries ago.
Many words have come to have completely different meanings in different Spanish-speaking countries. Some are so suggestive that El Pais's international edition has to monitor its headlines to avoid letting slip words like "concha" (shell) or "coger" (to catch or take) that are obscenities in Argentina. But the Chilean word for a horse race, "la polla", would be unprintable in a newspaper in Spain, where it means prick.
Much has been written recently about Spanglish, the patois of New Yorkers from Puerto Rico and the Dominican Republic. It's the same in Gibraltar where you hear things like: "Yo quiero un tube of toothpaste pero el pink one". (I want a tube of toothpaste but the pink one.") For some reason, the verb - where the action is - tends to stay Spanish.
If Spanglish is the infiltration of Spanish into English, for most of this century the process was the reverse: anything from "sandwich" to "modem" is now acceptable Spanish, even though technically a Spanish word cannot end in "m". If not yet in the dictionary of the Royal Academy of the Spanish Language, it soon will be.
Unlike their French equivalents, Spanish academicians see their role less as guardian and custodian of a precious heritage, and more as recorder and cataloguer of a common currency that has escaped their control. "The people always impose their language on the academy in the long run," says Carlos Mendo, editor of El Pais Internacional. "In the end, it has to cave in. It is flexible. After a few years they just incorporate the new words."
With 26 million Spanish- speakers in the US, it is hardly surprising that Spanglish is reaching even non-Spanish corners, that a chaplain the the US armed forces is called a padre even if he's a Protestant, and that "see you manana" is almost as common as "see you".
However, there are limits. One expression heard around the Tex-Mex border is "te llamo atras", a crude transliteration of "I'll call you back."
Mr Mendo shuddered. "No Spaniard would understand that," he said.