If you've read the last several issues of my Alternate History Newsletter, you've undoubtedly noticed that I've been trying to figure out a plausible way that the European conquest of the Americas could have been avoided. Ideally, the idea should not involve alien intervention, time-traveling South Africans with AK47s, or a very precisely aimed meteor bombardment. It should also allow Indians and Europeans to develop unchanged up until at least 1492, and hopefully until 1519, which I consider the more important date in terms of European conquest.

I think I may finally have a simple but effective point of divergence that would do what I've been trying to do with the other scenarios. What if some animal widespread in the New World carried a disease that was close to one hundred percent fatal to horses? Let's say the disease is a common bug that lives harmlessly in field mice. Back when there were North American horses, those horses were immune to it, having developed in the same disease environment. European horses have never encountered it, and it operates as a virgin field disease for them, killing off anywhere from 40 to 90 percent of the species on an large-area basis when it hits, and often killing an individual herd down to the last animal.

The field mice involved have not spread to the West Indies, so Spanish exploration and conquest of that area goes on as scheduled. The Spanish colony in Panama loses most of it's horses in the first couple of months after the settlement, and without the military edge that those horses gave them, the Spanish are eventually killed of forced to flee the mainland. That debacle has little impact on the rest of Spanish activities. Aztec Mexico is discovered on schedule. The two initial voyages of exploration don't last long enough for horses to be exposed to the disease.

Cortes and company land as scheduled. At that point it is just a matter of time before the disease strikes their horses. That actually takes a while. The Spanish spend a considerable amount of time on the coast, doing small-scale trading and assessing the military and political situation. Finally, Cortes decides to head inland and hopefully try to conquer the heart of the Aztec empire. As in our time-line, that takes him into Tlaxcallan territory, and into conflict with that warlike group. Shortly before that conflict starts, horses begin getting sick. Two are dead, and the rest very sick by the time the Tlaxcallans challenge the Spanish. Nevertheless, the Spanish ride the healthiest of the remaining horses into battle. That turns out to be a mistake. The horses are initially effective, but they tire quickly. The Tlaxcallans sense weakness, and surround the faltering horses, hacking them and their riders to pieces with razor-sharp obsidian 'swords' capable of hacking a horse's head off with one blow.

The destruction of the horses sends Tlaxcallan morale sky-high and demoralizes the Spaniards. Spanish foot-soldiers are far better armed and trained than the Tlaxcallans, but the Tlaxcallans have 50,000 men, while the Spanish have less than 500 men left. Each Spanish foot-soldier is not worth 100 Tlaxcallans, and without their cavalry the Spanish have no hope of winning the battle. The only question is whether or not the Spanish are going to be able to extract themselves from the debacle. In the short-term they do, but the Tlaxcallans pursue them in a running series of battles and eventually capture or kill all but a dozen or so of the Spanish.

Cortes proves his ability to land on his feet. He is captured by the Tlaxcallans, along with a couple of dozen other Spaniards. The Tlaxcallans eventually sacrifice all but four of the other Spaniards, but Cortes ends up marrying into the Tlaxcallan nobility and becoming a major factor in Tlaxcallan politics. The Tlaxcallans become much more formidable as they absorb a subset of the Spanish military and diplomatic playbook, and begin using captured Spanish weapons.

The Spaniards that escape think that Cortes and the other survivors are dead. The remnants of the men that marched inland, plus the ones that had been left behind on the coast, sail back to Cuba. The Spanish aren't done with Mexico. Ships from Cuba and Jamaica trade along the coast for the next year or so, while the Spanish prepare for a larger, more formidable expedition led by Narvaez. Smallpox makes the leap across the Atlantic on schedule and then makes the less difficult leap to Mexico. It spreads through the Aztec and Tlaxcallans, then heads to west coast of Mexico, and down through Central America, and to Inca Peru, just as it did in our time-line.

A large Spanish expedition under Narvaez attempts to establish itself in Mexico while the Aztecs are recovering from the epidemic, but again they lose most of their horses from disease. Narvaez is not the leader of men that Cortes was either. The expedition breaks up, and only a fraction of the Spanish make it home. Without horses, the Spanish simply don't have enough of a military edge to conquer Mexico, even while the Aztecs are weakened by disease.

So does this go anywhere my previous attempts haven't? Eventually the disease will spread back to the West Indies. It won't wipe out the horse population there, and a breed of horses will eventually emerge that is immune to it. The timing of that is very important. If the disease spreads to the West Indies within the first ten to twenty years, then the eventual outcome-European dominance of Mexico-is not likely to change, though the details may. If the Spanish aren't able to take horses to Mexico and have them survive by at least the early 1540's, history starts getting really changed.

What about Cortes and the Spanish survivors? Do they survive? Do they go native? Escape back to the West Indies? Create a hybrid Tlaxcallan/Spanish state?

What if our disease spread back to Europe? If most of the horses of Europe die, what happens militarily? Politically? Economically?

What do you think? Is this one worth pursuing?