The Inca Empire comprised multiple ethnic groups, some of which sided with the Spanish when they saw an opportunity.

“dictated to by a tiny elite of a hierarchy who would impose themselves over the entire system remember only a small number of people spoke Nahuatl the imperial language of the Aztecs only a small number spoke Quechua the imperial language of the Inca themselves it was the Inca Empire but it was constructed from multiple multiple different ethnicities and when they saw their chance they took it to side with the Spaniards”