It seems almost absurd to think about. I know that the historical consensus now is that disease is not really that big of a factor in new world conquest in the 16th century. But like, how could a band of a few hundred Spaniards conquer the huge empires of Central and South America.
Did they ever run out of ammunition and gunpowder? Wouldn't have taken a long time to reload?
I wrote a nine-part series on many of the common myths of conquest in another reddit community. The first three essays deal directly with what I believe is the heart of your question. I would also highly recommend Matthew Restall's short, readable introduction Seven Myths of the Spanish Conquest. I quote this book often in the series, and it helps to explain the complexity of a conquest that was anything but easy.
In the case of Mexico, indigenous allies (specifically Tlaxcalans) formed the bulk of the anti-Mexica forces led by Cortes. This is an interesting volume detailing the importance of indigenous allies. In the case of South America, disease and civil war in the Incan empire were a major cause. Again, the Spaniards were able to exploit internal political upheaval and gain important allies.
Where did you get the idea that disease is not a factor? I was under the impression upwards of 90% of the continent had died within a century of contact, with double digits dying within a few decades? Anthropology_nerd, what's this about disease not playing a big role?