When Columbus "discovered" The New World in 1492, he set into motion one of the most cataclysmic and important cultural exchanged in world history. The arrival of the Spanish in the New World had severe effects on the natives that lived there. The most notable of course is the introduction of deadly disease into the environment. Known as a Virgin Soil Epidemic, the spread of diseases such as smallpox killed an estimated 80% of all natives in both North and South America. It was mass eradication unlike anything that had come before it.
Other things were also exchanged. New religions arrived in the Americas and began chipping away at their own system of beliefs. The Spanish went to great pains to try and convert the natives, forcefully if necessary. New foods were sent back and forth. Items such as potatoes, turkey, tomatoes, vanilla, chocolate and corn arrived in Europe for the first time. In order to speed up the transfer of these item back to the old world, the Spanish employed an elaborate system of slavery which ended up working large portions of the population to death. When the supply of native slaves was gone, the Spanish began importing Africans, which resulted in the creation of entirely new cultures and races as the three groups interbred with one another.
Technology also revolutionized the New World. Gunpowder, metallurgy, horses and sailing technologies brought new possibilities to the natives as well as new concerns and fears.
This exchange of things between the new and old worlds was known and the Columbia Exchange.