|Columbus' First Journey. Image from Wikipedia|
Christopher Columbus did what other explorers failed to do. He added the Old World to an ancient world to create the New World. His discovery of the ancient world helped Nicolaus Copernicus to divorce astronomy from geography and destroyed early Christian-cosmos influenced ideas of world geography. Finally, his discovery led to the start of the Age of Discovery which ensured the importance of geography to world powers, merchants, and colonists. (His misadventure later on around Central America may even have given "America" its name).
Today his holiday is celebrated and despised in many ways. Even though Columbus was a proud man and poor administrator, and there were many ills committed by the European conquers of the Western Hemisphere, it is undeniable that Columbus' travels remade the world, remade geography, and allowed for great deeds to be accomplished in the truly New World.