In our own world, Spain sent Hernán Cortés and others to conquer the New World. Soldiers slaughtered civilians. Priests single-handedly destroyed nearly all of the written word of a culture in some ways more advanced than Spain’s, largely erasing it from history. And smallpox and other European diseases killed tens of millions of Native Americans.
In an alternate reality, a more enlightened Spain instead enters the New World as partners, negotiating a mutually beneficial co-existence with the Aztec, Inca and other native civilizations. Trust and respect rule the day, making both New World and Old World stronger for the sharing. Each culture shares knowledge the other lacks, to the benefit of all. Everyone holds hands and sings songs, and there is much rejoicing. Then, smallpox and other European diseases kill tens of millions of Native Americans.