The Conquistadors were the military explorers sent by the Spanish crown to the Americas to claim land, convert "heathens," and enrich both themselves and the crown. They were usually poor noblemen with few prospects back in Spain; in the first generation of explorers many were essentially unemployed knights. Some conquistadors simply launched expeditions to the New World without royal authorization, hoping to seize enough plunder to receive retroactive royal approval; official ones were obliged to turn over the “royal fifth” - 20% of all precious metals discovered or mined - of all loot to the crown.
The most significant conquistador was Hernan Cortes (1485 – 1547). A poor knight who had fought in the aftermath of the Reconquest as a young man, he jumped at the chance to travel to the New World. Cortes proved brilliant at manipulating the native groups he encountered in Mexico, where he arrived in 1519 with 450 Spanish troops and 15 horses. There, a powerful empire under the Aztecs had recently seized control of a large swath of territory. The Aztecs did not directly rule their subjects but instead demanded a constant flow of tribute, including captives who were destined for human sacrifice. Needless to say, the Aztecs were not popular with their subjects.
Working through a native translator, Malinche, who had already learned Spanish, Cortes was able to convince native groups resentful of the Aztecs to fight alongside the Spanish; practically speaking this meant that the native groups suffered most of the casualties. He fought his way to the Aztec capital of Tenochtitlan, where he was initially welcomed by the emperor Montezuma II. Once the Aztecs realized the extent of the rapacious designs of the Spanish they chased them from the city, but then an epidemic of smallpox undermined their ability to fight. Cortes was able to achieve the surrender of the surviving Aztec forces by 1522 and founded the Spanish colony of New Spain in the center of Mexico.
The other noteworthy conquistador of the first generation following Columbus was Francisco Pizarro (1478 – 1541). Inspired by Cortes’ success in Mexico, Pizarro set off (with 180 Spanish troops and 30 horses) for an empire the Spanish had learned of in the Andes of western South America in 1531. This was the Incan empire, also a relatively young state that encompassed territory along the Andes through present-day Chile, Ecuador and Peru. Pizarro ambushed the Inca emperor Atahualpa and captured him, demanding a building full of gold for his release. Instead, once the ransom was paid, Pizarro had the emperor killed and then marched on the Inca capital of Cuzco. By 1533, Spanish forces were in control of the empire and began sending enormous quantities of bullion back to Spain.
Thus, less than fifty years after Columbus's initial landing, the two greatest empires of Central and South America had already fallen to the Spanish. By 1600, practically every part of Central and South America was at least nominally under Spanish (or, in the case of Brazil, Portuguese), control.