I would also have to agree with the above post in that probably the greatest impact in the Americas was on the native people. Also The affect globally would be in the trade avenues that were opened up as a result.
I think in addition to the devastating impact on the indigenous people groups it is well worth considering the economic impact on Europe. Colonisation of the Americas and especially areas like Bolivia with immense natural resources such as silver funded Spain and enabled it to be a major player economically. You might want to research into Potosi, which is a famous Bolivian city because of the silver mines and all the silver that the Spaniards extracted.
In the Americas, perhaps the most important impact was on the native peoples. Those in the Spanish colonies were assimilated into Spanish society (at least those near population centers), but were relegated to the lowest levels of society. Their culture was not wiped out completely, but it was severly affected.
In North America, the natives were much less "lucky." They were simply pushed off their lands or killed outright in wars.
In both areas, there was pretty severe population loss because of European diseases.