This is covered in the article under the section "Native Allies": 'Diamond does not discount the fact that native allies assisted the Spaniards in seizing the

This is covered in the article under the section "Native Allies": 'Diamond does not discount the fact that native allies assisted the Spaniards in seizing the Americas. He is more concerned that Spanish victories should not be "written off as due merely [emphasis mine] to the help of Native American allies"' ... 'Diamond's suggestion is that Native peoples would have found it irrational to help tiny bands of Spaniards if they did not possess some military advantages.' ... 'When the Spaniards escaped Tenochtitlan, they numbered at most 1,300, many sick or wounded, along with just 96 horses. They were aided by 5,000-6,000 Tlaxcalans, who were unlikely to have many martial advantages over trained Aztec warriors. The city's population was estimated at the time to have been over 200,000. If just ten percent were fighting-age males, the Spanish faced difficult odds. A week later, at the battle of Otumba, 425 Spaniards and 3,000-3,500 Tlaxcalans defeated an Aztec force of 200,000—a feat that would still be impressive if the Spanish exaggerated their enemies' numbers by ten times.'