The biggest factor is that tons of people migrated to South America from Spain and Portugal--bringing their language, their customs, their culture, etc., with them. They then assimilated into the existing native cultures down there--sometimes peacefully, sometimes through war and domination--which resulted in a huge and very diverse mix of people from many parts of the world. Look up topics like "Spanish migration to South America," "Portuguese migration to South America," as well as "Spanish and Portuguese cultural influence in South America..." Also, remember worldatlas.com that I told you about--look up a few South American countries, and see the history of immigration into those countries. Hope this helps!
