I'm going to post in general terms about South American armed forces, please don't fire back over a few exceptions.
Do you remember the Falklands? The Argentine armed forces with many transcripts were very capable of invading the islands and sinking British shipping, but were not able to maintain their presence on the islands. The volunteer British forces were able to retake the islands with slightly newer technology and better training.
It is still the same today. While many of the South American nations have seen significant economic growth, and with their armed forces getting smaller pieces of their governments appropriations, their defence forces are still not up to a NATO standards.
Having said that, I want to say they fall short not in organization, but in equipment. Outside of Chile their air forces are near obsolete. Their naval forces are not brand new except for several diesel electric submarines, and their armies are mostly fitted with equipment a generation behind NATO.
Fortunately, their airmen, sailors, and soldiers are well trained, their leadership is up to par with NATO. While most of the South Aemerican armed forces are involved mostly with stabilizing their own nations, not being involved with any UN missions abroad, Brazil sent police forces to East Timor and Argentina sent a couple of ships to the Arabian Sea.
I have been involved in US sponsored Unitas exercises with these nations, and have been awed by their abilities to wage anti-submarine, anti-surface, and anti-air warfare with their ageing ships. Their patrol vessels are able to do the fishery protection, observe and enforce their customs, and do search and rescue missions.
If the South American armed forces were able to receive the funding of NATO nations for equipment and pay a salary equal to NATO personnel, I honestly believe they would be able to match NATO in quantity and quality. Unfortunately, all of these nations are developing economies.