The voyages of Christopher Columbus changed history because he led Europe west. In 1492 he landed in the Carribean and made contact with the new world. However, he did not realize this was a new world he thought he was in Asia. He made four voyages in all.
Soon many other nations of Europe began to send ships west. This started what we call in history the Columbian Exchange. The Columbian Exchange is when Europeans brought plants, animals, ideas, disease and other goods that were not in America before. And they took back to Europe the plants, animals that were only in the new world before.
The people of the new world and the people of Europe, Asia and Africa would never be the same. Either would the people of the new world, soon European nations would be fighting over the right to colonize in the new world. The native people of the new world would be devastated and the culture would struggle to survive.
As the first documented European visitor to the New World, consider what he brought west and took back home with him.
He and his men introduced diseases that ravaged the native populations, decimating entire cultures and civilizations. It was also the natives' first experience with European weapons, and the inherent racism the explorers carried with them.
By rediscovering the continent, Columbus set in motion a chain of events in Europe whereby others would follow in his footsteps, change permanently their concept of the world map, and start a long term imperial race to explore, exploit and settle the New World. Columbus started the gold fever which would grip Spain and bring the conquistadores to the Aztec Empire. There was no way to put the genie back in the bottle. Once discovered, a 500 year clash of civilizations would ensue, one which could not end in anything other than conquest of the natives.