. The USA practices the federal constitutional republic form of government while the UK uses constitutional monarchy and a parliamentary system.
2. USA has 50 states and one federal district whereas the UK is a single state kingdom comprised of four different countries.
3. The USA is more of a continent (a clumped piece of land) whereas the UK is more of an archipelago.
4. The USA has a bigger land area than UK, as well as, a bigger GDP or gross domestic product.
5. UK was a more powerful nation in the 19th century while the USA is the present most powerful nation in the world.
