Here's a short story:

New Spain () was a colonial territory of the Spanish Empire in the New World north of the Isthmus of Panama. It was established following the Spanish conquest of the Aztec Empire in 1521, and following additional conquests, it was made a viceroyalty (Spanish: "virreinato") in 1535. The first of four viceroyalties Spain created in the Americas, it comprised Mexico, Central America, much of the Southwestern and Central United States, and Spanish Florida as well as the Philippines, Guam, Mariana and Caroline Islands. 

After 1535 the colony was governed by the Viceroy of New Spain, an appointed minister of the King of Spain, who ruled as monarch over the colony from its capital, Mexico City. New Spain lost parts of its territory to other European powers and independence, but the core area remained under Spanish control until 1821, when it achieved independence as the Mexican Empire – when the latter dissolved, it became modern Mexico and Central America. 

New Spain developed highly regional divisions, reflecting the impact of climate, topography, the presence or absence of dense indigenous populations, and the presence or absence of mineral resources. The areas of central and southern Mexico had dense indigenous populations with complex social, political, and economic organization. The northern area of Mexico, a region of nomadic and semi-nomadic indigenous populations, was not generally conducive to dense settlements, but the discovery of silver in Zacatecas in the 1540s drew settlement there to exploit the mines. Silver mining not only became the engine of the economy of New Spain, but vastly enriched Spain and transformed the global economy. New Spain was the New World terminus of the Philippine trade, making the viceroyalty a vital link between Spain's New World empire and its Asian empire. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: Did the northern area of Mexico have a small population?
Guess: yes

Question: Did the Southern and central area of Mexico have a complex social and economic
Guess: yes

Question: Did the central and southern areas of Mexico have a small population?
Guess: no

Question: Did the Northern area of Mexico have many cities and settlements?
Guess: no

Question: What mineral was found there?
Guess: silver

Question: When?
Guess: in the 1540s

Question: Where specifically?
Guess: Zacatecas

Question: Who controlled New Spain beginning in 1521?
Guess: the Spanish

Now answer the following question in the same format.

Question: How many centuries did they retain control for?

three