From: A timeline where the USA fragmented after the American Revolution
Initial WI: What if George Washington hadn't died of a sudden illness in 1785?
POD: The states are unable to agree on a new Constitution, and the Confederation Congress is unable to resolve several serious disputes between various states. The USA fragments into 4 different countries by 1794.
TL: From Sea to Shining Sea - a history of a greater United States of America
"From Sea to Shining Sea" started as an fun freetime project and gradually grew into one of the most extensive, detailed, and controversial alternate scenarios ever posted on the internet. The basic POD is not terribly controversial - George Washington survives, and supports the creation of a new, stronger federal government that has the authority to effectively resolve the disputes between the various states. His support is crucial in persuading all of the states to eventually agree to this new, stronger government. The controversy comes from what happens to this large and relatively unified United States of America. In this scenario, it manages to gain control of a huge swathe of territory across the center of the North American continent, which contains parts of 7 different countries in the real world. By the early twentieth century, it becomes the world's leading industrial power, and two massive global-scale wars devastate or at least exhaust Britain, France, Germany, Russia, and China, allowing this enormous United States to become the world's dominant economic power in the second half of the twentieth century.
The many critics of this timeline argue that this alternate United States has more luck than is reasonably possible. To cite one widely-criticized example early in the timeline, in this scenario Napoleon forces Spain to cede the vast Louisiana territory back to France as in OTL, but then he turns around and sells the entire thing to the United States. This is not that implausible in and of itself - this larger and more United USA actually has enough revenue to make a large purchase, and Napoleon was reluctant to divert forces to try and support a colony that was largely cut off from France - but Britain simply stands by and allows the United States to more than double its territory without any military intervention. When war does come between the USA and Britain, it is started by the USA itself in what many would consider an insane attempt to seize Canada. This finally goads Britain into sending serious military force against the USA, but all of the British attacks ultimately fail to take their most important objectives, and the USA shrugs off the burning of its own capital city as if it never happened! Other events cited as especially improbable are Britain's willingness to concede large amounts of territory between the Pacific and Rockies to the USA, the complete victory of the United States government over an effort by no less than 11 of its own slaveholding states to break away and form a new nation, and the two massive global wars in the twentieth century which allow the already immensely wealthy United States to decisively swing the balance of power to one side while expanding its industrial might beyond the reach of any enemy weapons.
The timeline also has strong defenders, who tend to come disproportionately from North American countries. They feel that the critics, mainly from Europe, Asia, and South America, greatly underestimate the potential influence that a nation that encompassed the most productive areas of North America could have on world affairs. Debate about this timeline has sometimes degenerated into near-flamewars when North Americans accuse the critics of regionalist bias and anti-North American prejudice.