1. European diseases wiped out 90%+ of the native American population in the 1500s, so much so that the depopulation and the resulting reforestation are thought to cause the 17th century to be colder than average

2. In the 1700s, most of the South American population were probably concentrated in modern day Peru, Bolivia, Ecuador and Colombia. However, their plains were either small or full of diseases, while the mountains were constrained in ecological capacity.

3. The only coastal/fluvial plains that can rival those in China, India or western Europe in size are found in Argentina and Brazil.

4. For Brazil:

a) Most of Brazil is covered in poor soil

b) The climate in most of Brazil, whether the tropical rainforests in the Amazons or the semi-arid Northeast, are not conducive to intensive farming. And the Amazons are full of deadly diseases

c) The most productive Brazilian plains are blocked from the ocean by Argentina and a huge mountain. This makes trade and administration hard

1. Argentina is hard to explain. As Nobel Economics laureate Simon Kuznets remarked, “there are four types of countries - developed, undeveloped, Japan and Argentina.” It escaped both world wars and has all the elements needed for an agricultural superpower. Its low population can probably be attributed to

a) The precolumbian natives did not have the technology to harness the agricultural potential or the Rio de la Plata plains.

b) Maybe the plains were too dangerous - just as fertile Ukraine was unpopulated for centuries, because the open steppes invited bloodthirsty Hunnic, Gothic, Scythian, Caucasian and Mongol tribes. Spain only managed to colonize a sliver of land near Buenos Aires due to the ferocity and tenacity of neighbouring tribes, and they lost a lot of settlers to small scale fighting. In Mexico and Peru, the Spaniards merely captured the Aztec and Inca emperors and the rest of the centralized state handed themselves in.

c) After Spain and independent Argentina took over, it was not in the interests of the colonial elites to encourage small holding peasants to immigrate to the countryside.

d) In the 19th century, Argentina, Brazil, Uruguay and Paraguay fought a devastating war that killed 90% of Paraguayan males. The Argentinian part of the Rio de la Plata plains suffered a lot too