The sixteenth, seventeenth and eighteenth centuries changed the world in dramatic ways. But probably, the biggest change the world saw or has ever seen, was the finding and conquest of the Americas. Many are the theories as to what led both the Spanish and Portuguese empires to seek these voyages, but the truth of the matter is that the main reasons that pushed Spain to support Cristopher Columbus in his trip in 1492 were, first, the desire to discover and open new trade routes to the Indies. And the second reason was evangelization, which the two Spanish moarchs believed would be empowered by colonization.
When the Spanish first arrived in the Americas, their first encounter was not with any big Native tribes or settled civilizations. It was not until later on, in 1519, that the Spanish encountered true Native American civilization. And the first to find this was Hernán Cortés, who between 1519 and 1521, led a war against the Aztec Empire, one of the biggest and most important of the entire continent. The Aztecs were settled in the Gulf of Mexico, in what is today Mexico itself. The Aztecs, led by Moctezuma II were really advanced people, with a federal-like way of government, cities, technology and an organized society. But like all well-organized and advanced societies, problems arose. The first was that through contact with the Spanish, many diseases unknown until then diminished the number of Natives and also because of weaponry, which allowed the Spanish to finally overcome the Aztec forces.
The second empire was the Inca Empire, in what is today Peru, specifically in Cusco. Unlike its sister empire in Mexico, the Incas did not have wheeled vehicles and they did not use farm animals. They did not have a currency and they survived on exchange of goods, instead of a market. What made them really advanced was their ability in masonry and the use of stone. Their architecture was really advanced and like the Aztecs, their cities were impressive. They also had a centralized system of government led by a king, who at the time of the arrival of the Conquistadors was Atahualpa and the king was considered the owner of everything within the empire. They also had a very advanced system of roads that connected the central city of Machu Picchu with the rest of the Empire. It was Francisco Pizarro who in 1526 moved from Panama to the Andean region and found himself at Machu Picchu. After several trips, finally, between 1532 and 1533, Francisco Pizarro and the Spanish were able to take control of the vast Inca Empire.
In the end, most of the Americas, save what is nowadays Brazil, that ended in the hands of Portugal, became part of the enormous Spanish Empire. The result was a group of colonies from which the Spanish derived the precious metal of gold and which made them really rich. The Natives, at first were enslaved by the Spanish until through intervention of the Church, black people were brought in to prevent the death of the Natives. Disease also decimated the Native population in the Americas. There was a lot of racial mixing betwen the Spanish and Natives, which gave origin to many new skin colors, typical of Spanish America.