South America is a challenging region to play. It has two concentrations of Cities one in Mexico and another in south Brazil. It is best to stick to defending South America by placing your silos in a circle with one radar in the center. Put this formation some were in the Amazon so that you will be able to defend as much of South America as possible while still defending your cities in south Brazil. In order to defend Mexico it is best that you ally with North America because their defenses often overlap with Mexico.