In any case, Colombians may bear a teeny, tiny, little grudge towards Americans because of their prosperity . As a country, Colombia has many problems. And USA has just apparently breezed by and taken a place as a world power. And kept the drug problem in check by keeping close eye on Colombian imports. Not good for Colombia's economy.
Students are all aware of USA's power.
Most students keep in touch with the current events in history, and care very much about the future of their country. They have been taught that their country is bad off because they, as uncaring citizens, have done nothing to better the situation. So a seedling of guilt is in everyone. Technically, America is the whole package, North and South America. By calling USA America, Colombians will feel you are intentionally leaving them out, thinking of them as insignificant.