What If Muslim Spain or Ottoman Empire Colonizes Centuries Before Columbus?

If Muslim Spain or the Ottomans reached the American continents, that would be a big change. I don't know about genocides, but diseases would still affect a number of the Indians simply for the fact that they're not immune to the European diseases. I was reading a history book where it talked about how the Spanish conquistadors unwittingly caused the depopulation in northern America which made it easier for British settlers to move in a century or so later.

Do you think either of those two powers would cause the food transfers of things like potatoes back to Europe? Or perhaps spur earlier colonization efforts by the Scandinavians, English, French, and Germanic nations? Interesting thoughts.

I am rather skeptical Muslim conquest would have been much better for Amerindian peoples than the European one, for various reasons. First, there is no saving them from mass dying due to sheer lack of immunity to Old World diseases. Second, conquest of the Western Hemisphere and destruction of its Precolombian civilizations by the first imperialist Eurasian civilization to break the Age of Exploration threshold was more or less as unavoidable as the pandemic short of very contrived circumstances due to the vast technological gap that Precolombian cultures had developed with the sophisticated Eurasian ones, be them Europeans, surviving Romans, Muslims, Chinese, Japanese-Koreans, or Indians to quote the most likey candidates. Third, Islamic culture was just as enthusiastic a practitioner of slavery with an ethnic prejudice angle as the Europeans, and/or just as likely to enhance and entrench it because of ideological pressure to justify the gains of plantation economy. Fourth, the Muslims were just as likely to be intolerant of 'pagan' cultures as the Europeans, especially once they get horrified by the extensive and systematic use a few of them made of human sacrifice.

All in all, if you are looking for a 'least evil' Eurasian civilization to be the (inevitable) colonizer of the Americas, my vote goes to a surviving Rome that overcame the causes of its OTL decline, absorbed all of Europe and the Middle East, and mastered Renaissance technology. Roman civilization entirely based its notion of identity on a civic ideal, was alien from ethnic prejudice and willing to give an equal place at the table to anyone that bought in its deal, was world champion in assimilating conquered peoples, and its model of slavery (assuming it would be still thriving when they discover the New World, which is doubtful) was completely separate from racial prejudice and provided a demonstrably effective path to integration of freedmen in society. Roman model of conquest usually prioritized assimilation of conquered peoples rather than genocide. They were far from averse (and rather efficient) at pragmatically using it as an extreme method of quelling resistance to their rule, but not any more so than your typical imperialist civilization.

Admittably, there would be no saving Precolombian civilizations from pandemic mass dying or violent conquest at the legions' hands, nor from Romans doing their best to stomp out cultures that resisted their rule too hard or practiced human sacrifice. But in their wake, you would get mass assimilation of pacified Amerindian disease survivors in the Roman Empire as equals and their fusion by intermarriage with the many settlers that are surely coming to the Western Hemisphere from crowded Roman Europe (well, the ones that are not going to the other Roman colonies in Russia and East Africa, anyway). In a few centuries, the Roman elites and middle class are surely going to sport lots of brown-skinned faces as it befits the considerable demographic and economic weight of the American provinces, and nobody is going to bat an eye at their skin color or the quality of their ancestors. They shall be as true and proud Roman citizens as the Europeans, Middle Easterners, and Africans.

This is pretty much what happens in my own Roma Aeterna TL. Slavery was in terminal decline by the time (10th century AD) Rome crossed into its Renaissance stage and its explorers came to the New World shores. It was gradually getting restricted to the modern use of main punishment for serious crimes that did not get the death penalty. Just like all the other major conquest bouts during Rome's expansion, colonization of the Americas caused a temporary revival of slavery, but its decline resumed once things got settled, with no stigma attached to descendants of freedmen. To the degree the Romans felt necessary to use unfree labor to run colonial economy, in the end they mostly resorted to indentured servitude from whatever manpower source available. Roman civilization was so alien from ethnic prejudice that one more conquest among many, albeit bigger than most, made no difference.

Roman conquest of the Americas was no doubt violent and bloody, but invariably followed by efficient pacification and genuine assimilation. Just like anyone in the space between the Atlantic, the Sahara, the steppes, and the Indus before them, and the natives of Gothia (TTL Russia-Ukraine) and East Africa at the same time, Amerindian survivors of the contact pandemic learned Latin, converted to Romanism and/or Buddhism (*), developed a taste for bath houses, and became proud and loyal Roman citizens. They mingled with the many settlers that came to the American provinces from teeming Roman Europe. In time, the Amerindian natives and the European settlers part intermarried, part settled down to be good neighbors under the aegis of Pax Romana. Being true to their template, the Romans were eager to adopt anything useful they found in the Americas, and just as willing to share the achievements of their civilization with friendly natives.

By modern times (**), citizens of the Empire are culturally and politically indistinguishable across the Western Hemisphere and the Old World, and their exact admixture of Caucasian, Amerindian, African, or Asian blood makes no meaningful difference for anyone (except perhaps when dealing with certain genetic disorders). The extant issues modern Rome faces (superpower competition with the Chinese and Indian empires, socio-economic inequality, power imbalance between the elites and the lower classes, environmental issues from mature global industrialization, space colonization, transition to a postcyberpunk-interplanetary civilization) have little to do with bigotry. When they hear about 'colonization', the average Roman, Chinese, or Indian thinks about the final frontier in space, not insignificant details about the lot of anybody's ancestors long ago. This world's history and culture since the Iron Age were largely shaped by a few Eurasian imperial civilizations that stayed successful and kept a recognizable identity since antiquity, besides inevitable social change. The occasional bout of disunity and strife was universally recognized as a bad thing and invariably recovered from. They recognized each other as equals long ago, and grew in parallel to account collectively for the vast majority of world land area, population, and economy by modern times. Therefore, the notion their imperialism was anything but a beneficial force of order and progress is a major outrage to common sense for this world's culture. They regard the balance of Pax Romana, Tianxa, and the Indian equivalent as the natural state of things.

(*) Romanism is TTL Rome's majority religion, a philosophically sophisticated syncretist evolution of European polytheism with major pantheist and monist elements, a broad analogue of Hinduism with European memes and no caste system. Buddhism peacefully shares space with it as the second most important religion, and secular humanism largely makes up the rest. During its evolution, Rome either decided the Middle Eastern monotheisms were alien, hostile, and dangerous to its civilization and ruthlessly wiped them out, or its very success prevented them from arising. Later, the Romans resolved the cultures that indulged in such barbaric practices as human sacrifice, cannibalism, and/or genital mutilation deserved the same fate of extinction.

(**) In terms of a technological equivalent to the Information Age on the edge of transition to postcyberpunk-interplanetary. Since TTL Europe never experienced a collapse and stayed as dynamic as OTL, and the world's leading civilizations grew in parallel thanks to their exchanges and competition, they achieved our level centuries ago, and were significantly more advanced in most fields by then. By the 21st century AD, in all likelihood TTL Rome is a broad equivalent of the Romulan Star Empire of Star Trek, without any taboo about transhumanist technology.