The Columbian Exchange involved the interchange of disease, technology, culture, and agriculture between the New and Old Worlds after Columbus's expeditions in the late 1400s. The exchange had some positive features, such as the introduction of new animals in the New World and new agricultural products in the Old World, as well as some very negative effects such as the diseases and guns brought to the New World.
Europeans introduced animals, such as the horse, in the New World, that would go on to change Native American culture and even become central to Native Americans' hunting and living practices. However, some plants and animals brought to the New World forever upset the natural ecosystem.
The European part of the exchange had several negative effects. For example, the Spaniards also introduced the encomienda system that resulted in subjugating native people and making them work in exchange for the idea that Spaniards were saving their souls through Christianity. Other Europeans also subjugated native people. The most devastating import of Europeans was their unwitting transmission of diseases, such as smallpox, to natives who had never experienced these diseases and therefore did not have immunity. Smallpox decimated many native populations. In addition, Europeans brought slavery to the New World, with devastating and inhuman consequences. The Europeans enforced their practices with guns--a negative outcome of the exchange.
The New World was the source of many new products for the Old World, including corn, tomatoes, potatoes, pumpkins, and tobacco. In particular, tobacco became very popular in Europe, and Europe imported sugar from the New World as well. These products provided a boon to the European economy--a positive effect of the exchange.
Another result of the Columbian Exchange was racial mixing, as Europeans married natives, and later, slaves also intermarried or had children with European descendants and native people. The result was the creation of the New World and its unique and varied population.