During the 15th and 16th centuries, leaders of several European nations sponsored expeditions abroad in the hope that explorers would find great wealth and vast undiscovered lands. The Portuguese were the earliest participants in this “Age of Discovery,” also known as “Age of Exploration.”

Starting in about 1420, small Portuguese ships known as caravels zipped along the African coast, carrying spices, gold and other goods as well as enslaved people from Asia and Africa to Europe.

Other European nations, particularly Spain, were eager to share in the seemingly limitless riches of the “Far East.” By the end of the 15th century, Spain’s “Reconquista”—the expulsion of Jews and Muslims out of the kingdom after centuries of war—was complete, and the nation turned its attention to exploration and conquest in other areas of the world.

Christopher Columbus, the son of a wool merchant, is believed to have been born in Genoa, Italy, in 1451. When he was still a teenager, he got a job on a merchant ship. He remained at sea until 1476, when pirates attacked his ship as it sailed north along the Portuguese coast.

The boat sank, but the young Columbus floated to shore on a scrap of wood and made his way to Lisbon, where he eventually studied mathematics, astronomy, cartography and navigation. He also began to hatch the plan that would change the world forever.

At the end of the 15th century, it was nearly impossible to reach Asia from Europe by land. The route was long and arduous, and encounters with hostile armies were difficult to avoid. Portuguese explorers solved this problem by taking to the sea: They sailed south along the West African coast and around the Cape of Good Hope.

But Columbus had a different idea: Why not sail west across the Atlantic instead of around the massive African continent? The young navigator’s logic was sound, but his math was faulty. He argued (incorrectly) that the circumference of the Earth was much smaller than his contemporaries believed it was; accordingly, he believed that the journey by boat from Europe to Asia should be not only possible, but comparatively easy via an as-yet undiscovered Northwest Passage.

He presented his plan to officials in Portugal and England, but it was not until 1492 that he found a sympathetic audience: the Spanish monarchs Ferdinand of Aragon and Isabella of Castile.

Columbus wanted fame and fortune. Ferdinand and Isabella wanted the same, along with the opportunity to export Catholicism to lands across the globe. (Columbus, a devout Catholic, was equally enthusiastic about this possibility.)

Columbus’ contract with the Spanish rulers promised that he could keep 10 percent of whatever riches he found, along with a noble title and the governorship of any lands he should encounter.

On August 3, 1492, Columbus and his crew set sail from Spain in three ships: the Niña, the Pinta and the Santa Maria. On October 12, the ships made landfall—not in the East Indies, as Columbus assumed, but on one of the Bahamian islands, likely San Salvador.

For months, Columbus sailed from island to island in what we now know as the Caribbean, looking for the “pearls, precious stones, gold, silver, spices, and other objects and merchandise whatsoever” that he had promised to his Spanish patrons, but he did not find much. In January 1493, leaving several dozen men behind in a makeshift settlement on Hispaniola (present-day Haiti and the Dominican Republic), he left for Spain.

He kept a detailed diary during his first voyage. Christopher Columbus’s journal was written between August 3, 1492, and November 6, 1492 and mentions everything from the wildlife he encountered, like dolphins and birds, to the weather to the moods of his crew. More troublingly, it also recorded his initial impressions of the local people and his argument for why they should be enslaved.

“They… brought us parrots and balls of cotton and spears and many other things, which they exchanged for the glass beads and hawks’ bells," he wrote. "They willingly traded everything they owned… They were well-built, with good bodies and handsome features… They do not bear arms, and do not know them, for I showed them a sword, they took it by the edge and cut themselves out of ignorance. They have no iron… They would make fine servants… With fifty men we could subjugate them all and make them do whatever we want.”

Columbus gifted the journal to Isabella upon his return.

About six months later, in September 1493, Columbus returned to the Americas. He found the Hispaniola settlement destroyed and left his brothers Bartolomeo and Diego Columbus behind to rebuild, along with part of his ships’ crew and hundreds of enslaved indigenous people.

Then he headed west to continue his mostly fruitless search for gold and other goods. His group now included a large number of indigenous people the Europeans had enslaved. In lieu of the material riches he had promised the Spanish monarchs, he sent some 500 enslaved people to Queen Isabella. The queen was horrified—she believed that any people Columbus “discovered” were Spanish subjects who could not be enslaved—and she promptly and sternly returned the explorer’s gift.

In May 1498, Columbus sailed west across the Atlantic for the third time. He visited Trinidad and the South American mainland before returning to the ill-fated Hispaniola settlement, where the colonists had staged a bloody revolt against the Columbus brothers’ mismanagement and brutality. Conditions were so bad that Spanish authorities had to send a new governor to take over.

Meanwhile, the native Taino population, forced to search for gold and to work on plantations, was decimated (within 60 years after Columbus landed, only a few hundred of what may have been 250,000 Taino were left on their island). Christopher Columbus was arrested and returned to Spain in chains.

In 1502, cleared of the most serious charges but stripped of his noble titles, the aging Columbus persuaded the Spanish crown to pay for one last trip across the Atlantic. This time, Columbus made it all the way to Panama—just miles from the Pacific Ocean—where he had to abandon two of his four ships after damage from storms and hostile natives. Empty-handed, the explorer returned to Spain, where he died in 1506.

Christopher Columbus did not “discover” the Americas, nor was he even the first European to visit the “New World.” (Viking explorer Leif Erikson had sailed to Greenland and Newfoundland in the 11th century.)

However, his journey kicked off centuries of exploration and exploitation on the American continents. The Columbian Exchange transferred people, animals, food and disease across cultures. Old World wheat became an American food staple. African coffee and Asian sugar cane became cash crops for Latin America, while American foods like corn, tomatoes and potatoes were introduced into European diets.

Today, Columbus has a controversial legacy—he is remembered as a daring and path-breaking explorer who transformed the New World, yet his actions also unleashed changes that would eventually devastate the native populations he and his fellow explorers encountered.