What four countries make up atlantic south america?

Following four countries make up Atlantic South America;

1: Argentina

2: Brazil

3: Paraguay

4: Uruguay

Atlantic South America as it has been manifested above consists of these four countries. Atlantic South America basically occupied almost 2/3 or 67% of the whole South America where only Brazil captures approximately half of that entire continent. The physical features which can be seen in the entire South America are also very much visible in these four countries.