If I am writing a sentence and it reads: In this paper we will be comparing exports and imports in South American countries. Do you spell countries or country's?
I'm not a professional teacher, but the plural of "country" is "countries". The word "country's" is most commonly a singular possessive. So, one could write "There are are not many countries in South America without a coastline" but, "Brazil grows a lot of coffee and the country's economy is dependent on the income from coffee exports."