OMG what is this thread.
It simply couldn't happen. Any diseases of similar lethality to what the Europeans brought would wipe out the explorers before they'd have a chance to return. They'd all die in transit and their ships would be lost at sea.
Because every single Native American died of European diseases and isolation was the only way any of them survived, right?
This motherfucker made the journey across the ocean
twice, and still fell over to disease in the end. How about that?
Okay, then... Using Wikipedia's numbers, the so-called Black Death killed between 30-60% of the population of Europe. This is going to kill less, only 20% of Europe and North Africa.
It's going to do one of two things, it's going to terrify the Europeans into abandoning the Americas entirely as a land of Hellspawned Disease and Death or it's going to utterly enrage them and make the Americas the focal point of all future Crusades for the exact same reasons.
In the 1520s, smallpox hit Mexico so hard that it was recorded that in some regions, half the population just straight-up died over the course of less than a decade, and records indicate that the epidemic originated with
one dude. In the following hundred and fifty years,
90% of the population died from disease. Most of the early New England settlements were essentially just built directly atop coastal villages which had been more or less entire wiped out, often so quickly that European settlers straight-up picked up the agricultural processes from where native efforts left off. So many native Americans died that the regrowth of trees cleared for agriculture across the continents might have caused
the Little Ice Age.
The Black Death was bad, but what tuberculosis and smallpox did to the Americas was apocalyptic. There's not going to be any fucking
crusades, because Europe is going to be blasted back centuries worth of infrastructure and population growth. Not to mention the complete collapse of every political system in Europe, seeing as one of the prime effects of virgin soil epidemics is that the nobility consistently get fucking
shredded by the outbreak.
Oh, and that's not all! You can kiss the vast majority of European economic growth post-contact goodbye, because the most critical and most underestimated element, the cultivation of American agricultural staples like corn and potatoes
probably ain't happening. That means that Europeans are probably still going to be mostly growing their much less hardy crops through this period.
Nevermind what these diseases are going to do to China, cuz China didn't do so hot when the Black Plague hit them either, and in some places like dense cities they were hit even harder.