The Columbian Exchange took place as a result of the European colonization of the Americas. The transfer of culture and biology between the Old and New World that characterizes the exchange began when Christopher Columbus arrived in the Caribbean Islands in 1492.
After its separation millions of years ago from a landmass containing Eurasia and Africa, the American continent experienced a period of ecological isolation. As a result of this isolation, its ecosystems evolved separately and took on different characteristics to those found elsewhere in the world.
Following Columbus' arrival, many of the European nations were interested in colonizing the newly discovered land and sent men in ships to conquer territory, find gold and convert the local people to Christians. With the arrival of these foreign colonizers, the native people living in the Americas were exposed to not only European people and their culture for the first time, but also to new varieties of animals, plants and diseases.
Similarly, the European colonizers were also exposed to biological and cultural elements that did not exist in the Old World. This exchange between the continents was completed when returning Europeans took home with them the goods and microorganisms particular to the American continent.