The most important voyages of discovery of the early modern period were undertaken by agents of the Spanish monarchy, starting with that of Christopher Columbus in 1492. They were inspired by religious fervor as much as a practical desire for riches – fresh off the successful Reconquest, Queen Isabella agreed with Columbus’s vision of flanking the Muslim forces of the Middle East and recapturing the Holy Land as much as she also wanted new trade routes to Asia. The voyage was thought to be feasible both because all educated people already accepted that the world was round (common knowledge since the days of ancient Greece) and because the circumference of the globe was not really clear to them; it simply was not known how long one would have to sail west to reach the east.
Columbus himself had totally inaccurate beliefs about the distance between Europe and Asia – he based his geography on an ancient (and completely inaccurate) account by the Greek philosopher Ptolemy and he thought that Asia was not far west of Europe. Despite being disliked and distrusted by most of the rulers he had approached in the past, Columbus succeeded in winning Isabella over to his vision, and she paid to outfit him with a tiny fleet (she sent him with letters of introduction to the Great Khan, who she presumed still ruled in Asia). Columbus departed in August of 1492 with three small boats – the Niña, Pinta, and Santa Maria - and 90 men. They arrived in the Bahamas in October.
Columbus ended up spearheading everything the Spanish empire was to represent in the Americas: brutality against the native “Indians,” attempts to convert Indians by force, intense greed for precious metals, and the introduction of pathogens against which the native people had absolutely no resistance. With Columbus, the traffic in goods and commodities between the two hemispheres began. While Europeans at the time were obsessed with the vast mineral wealth found in the Americas, it is clear in historical hindsight that far more important than precious metals were the living things exchanged between the western and eastern hemispheres of the globe starting in 1492. Historians now refer to that enormous distribution of plant and animal species, as well as bacteria and viruses, as the Columbian Exchange.
From the New World, Europeans brought back corn, potatoes, tobacco, chocolate, and tomatoes, just to name the most important of the crops that soon flourished across Africa and Eurasia. From the Old World, Europeans imported all of the large domesticated animals - horses, cows, sheep, goats, pigs, and sheep - as well as numerous crops like rice, wheat, sugarcane, and coffee. Potatoes alone would go on to reshape the demographics of all of northern Europe and various other regions in the world because they provide a great deal of nutrition and calories and can grow in poor, rocky soils. The poor of many European regions (Ireland, most famously) became largely dependent on potatoes for nourishment by the eighteenth century.
That noted, the single most significant biological entity to be exchanged between the hemispheres was the smallpox virus, which was at the heart of the worst epidemic in world history. Isolated from the western hemisphere for thousands of years, Native Americans had no resistance to Eurasian diseases. Because almost all diseases that affect humans are mutated strains of diseases affecting domestic animals, referred to as zoonotic diseases, and all of the large animal species that can be domesticated were Eurasian in origin except llamas, Eurasians and Africans had spent thousands of years both suffering from and building up resistances to epidemics while Native Americans did not. Those epidemic pathogens arrived all at once with the European invasion of the New World that began with Columbus.
Historians refer to the demographic catastrophe that accompanied the European encounter with the Americas as the Great Dying. As much as 90% of the native people of the Americas died within a few generations of Columbus’s arrival. While the Spanish and Portuguese did win some noteworthy military engagements with native forces, due largely to their use of steel weapons and horses, their true military advantage lay in germ warfare, something they certainly did not anticipate unleashing on their arrival. Spanish explorers in the early sixteenth century encountered whole vast swaths of land with abundant evidence of sophisticated cultures that were already abandoned, their former inhabitants decimated by disease. In other words, the conquest of the Americas by Europeans was shockingly swift not because Europeans were significantly more militarily powerful than were Native Americans, but because most of the latter were already dead thanks to disease.
The Columbian Exchange, and the Great Dying that was part of it, began with Columbus’s initial voyage. Almost immediately after Columbus's return to Spain after his expedition, Ferdinand and Isabella of Spain grasped the significance of his discovery and actively funded more expeditions and, soon, colonists. The Spanish crown also quickly tried to cement its hold on the New World – they petitioned the pope to grant them everything across the Atlantic. After papal intervention and negotiations between the Spanish and Portuguese, the Spanish were to receive everything west of an arbitrary line on the map 1,100 miles west of the Cape Verde Islands, with everything to the east granted to the Portuguese. Practically speaking, this meant that the Portuguese concentrated their colonization efforts on Brazil, Africa, and India, while the Spanish concentrated on the Caribbean, Central America, and South America. Needless to say, the other European powers were not about to honor this agreement, called the Treaty of Tordesillas and dating to 1494, but it gave the Spanish and Portuguese a considerable head start.
By the 1520s, Europeans recognized that Columbus had been completely wrong about the New World being part of Asia. The term "America" was invented by another Italian, Amerigo Vespucci, who was another early explorer (he led two expeditions between 1497 and 1503) and the first to grasp the immensity of the western hemisphere. Vespucci coined the phrase "New World" in the first place, hence “America” rather than “Columbia” – Vespucci’s accounts were printed first. He was also a relentless self-promoter, whereas Columbus did not attempt to publicize his discoveries with the same focus.
Even though Europeans quickly realized that the Americas were whole new continents, they persisted in their quest to find a western route to Asia. The Spanish dispatched explorers and sailors who sought Asia by going around the Americas, even as they were also busy conquering the great empires of the Aztecs and Incas. This led to the voyage of Ferdinand Magellan (1480 – 1521), who commanded a small fleet of five ships funded by the Spanish crown and tried to find a western route to Asia in 1519. He succeeded in rounding South America and crossing the Pacific, but was then killed by natives of the Philippines in 1521. The remnants of his fleet limped back to Spain in 1522, proving that it was possible to sail around the world. The Spanish would subsequently use the Philippines as the basis of their Pacific trade network, ultimately linking together Europe, the Americas, and Asia and fulfilling the original vision of a western route to Asia that had inspired Columbus’s expedition in the first place.