The United States of Amerindia (Horses in America)

Point of Divergence
In this alternate scenario, horses aren't driven to extinction in the New World at the end of the last Ice Age. Instead of hunting them, early Amerindians learn to tame and domesticate the horse, giving rise to new technologies and societies. With the horse and the dogs brought from Polynesia and Siberia, early natives begin to herd and domesticate more animals they couldn't have in our timeline, such as bison, white-tailed deer, and pronghorn. This influx of domestic animals, along with the already abundance of crops(maize, legumes, potatoes, tomatoes, cacao, berries, etc.) and the other domesticate animals(turkey, llama, guinea pig), huge societies and cultures sprout across the continent. They flourish throughout the Bronze Age, outliving their Old World counterparts, like Mesopotamia, Sumer, and Minoan Greece. The domesticate animals cause the building of great cities, and the evolution of newer, deadly strands of disease, such as Lyme Disease(from deer), Avian Flu(from turkey and passenger pigeons) and more. Nations like the Iroquois, Cherokee, Lakota Sioux, Zuni, Mississippi, and Navajo still form their nations, but with better technology and cities, and even writing systems.

European Exploration
When Europeans arrive, they do not find any tribes or hunter-gatherers, but complex farmers and nations to rival those of Rome. Armed with stronger immune systems used to avian flu, cowpox, and related diseases, the natives take a heavy hit from Old World plagues, but only loose 35% of their population, whilst giving Europeans diseases that wipe out nearly 45% of people in the Old World. Ages of warfare prepare the natives to easily fend off the Europeans, decimated by disease, and cut off from a steady influx of supplies to maintain war. In after centuries of warfare with the Europeans, the Iroquois, itself a nation of five united tribes, sent delegates across the continent to form a large federation like their own, to fend off the European invaders and conquistadors. Since the horse allowed for communication to be easier, the major nations, the Iroquois, Navajo, Lakota Sioux, Cherokee, Miami, Zuni, Mississippi, Pueblo, and the Pacific Northwest, all felt a similar cultural identity, and need for shared defense.

Rise of Amerindia
A great council was held in what in our world is Kansas City, near the center of the continent, to form the longhouse of representatives for the nine nations people, with a government mirroring that of the United States of America. Here, a Cherokee representative, a scholar named, Sequoia, offered to call the union, "Amerindia", as the natives, were split on whether to let themselves be called Indians from India or Americans from America, by the European powers. The name was adopted, along with a flag. The flag has two blue vertical bands on both sides, representing the Atlantic and Pacific, which border a brown square at the center, representing the land. The nation's shield is nine arrow(for each nation respectively) held together by a string(representing the union and strength of bonding), underneath a maple tree that a bald eagle is perched in(representing love of nature and national pride). The flag is finished off with the two halves of a broken tomahawk laid diagonally on opposite sides of the shield, representing peace. And thus, with the ratifying of their constitution in 1776(in their calendar), the United States of Amerindia, is born.

The Seven Years War
With no colonies in the Americas, the Europeans rely on Amerindia, the main power, and their allies(the Aztec Empire, Ottawa(Canada), Nunavut(Greenland), and Inca, for free trade of exotic goods. Britain tries several times to invade Amerindia, but armed with clumsy rifles far away from familiar territory and with no contact with the homeland, are easily swept back into the Atlantic. Amerindia designs new technology, based on native ideals and European technology. One such is the first missile system, a ballista of iron frame and fiber string, shooting carved branches up to 10 feet long tipped with iron capsules of gunpowder, over 100 feet away, rivaling the cumbersome cannons of Europe. Also invented are agile war canoes armed with miniature ballistas that could out-maneuver western ships. As war erupts in Europe, Amerindia convinces its allies to stay out of conflicts and remain industrial but neutral unless provoked. At the end of the eighteenth century, open trade and zero international conflict create a high standard of living, good education, and make the New World Order of Neutrality(the alliance), especially Amerindia, global powers. The nations also become religiously tolerant, as many of the tribes had different religions, and become a safe haven for sizable Old World religious minorities.

World Wars
Amerindia and it's allies are completely neutral and isolated from the conflict of the first world war. The Great Depression hits, but with a fertile great plains area, the nation can provide welfare food for the impoverished, and the next president or Chief in Command, Hiawatha VI, is credited with bring the country out of the economic crisis with his own new deal programs. The country and its alliance continued to be neutral in World War II, as the powers were cut off from any conflict in Eurasia, until Germany and Japan launched a secret military plan to try and take the Americas out of the war equation, with Nazi Germany attacking a port in Nunavut, and the Japanese bombing the Kingdom of Hawaii, a Polynesian ally based for Amerindia, in 1942. Immediately, the major powers took offense, and with their powerful militaries, quickly wiped out Nazi Germany and Imperial Japan.

Cold War and Beyond
The American allies, though involved in politics and trade, remained unaligned in global and military affairs following the second world war. The Soviet Union tried an unsuccessful invasion of Alaska(territory of Ottawa), and the country continued to innovate, though never getting involved in nuclear weaponry. Today, the country of Amerindia itself is a world power, and its allies benefit from it. The future is uncertain, but Amerindia is stable and sure footed enough to last.

Alliances
Amerindia had always felt distant from any influence from the Old World, and only ever allied itself with European powers like Britain and France near the end of WWII. It mainly stays out of heated politics, prefering to focus inwardly with other American powers, and outwardly in trade. Politically, it has borders almost identical to those of the USA.

Amerindian Constitution
The constitution provides many of the similar rights and freedoms as the United States in our world, such as religious freedom, speech freedom, no slavery, and so on. All citizens are equal under the law. With many being spiritually connected to nature, it is illegal by constitutional law to harm or touch an organism marked as endangered or sacred, as they are counted as the sovereignty of Amerindia.

Demographics
Though mainly Amerindian(several tribes and ethnic groups), the nation also has sizable western minorities, such as African ethnic groups(escaped slaves and descendants) and Europeans.