I would argue that the permanent US objective in Latin America was to keep the area stable and unthreatening to the US. This can be seen particularly in the Monroe Doctrine.
The Monroe Doctrine said that European countries should not try to take any new colonies in the Americas. It said that any European interference in the affairs of the Latin American countries would be deemed a threat to the security of the US. By saying this, the US was essentially arguing that Latin America was its own sphere of influence and that anything that happened there was important to the US.
By creating the Monroe Doctrine, the US made clear that it valued stability in Latin America and it wanted to keep any potential European enemies from gaining a foothold in the region.