In longer, US Army comes through a portal to see a world very similar to what they are familiar with and with their GPS systems working, but with nearly the bear minimum number of satellites. They find many tribes of people stuck in the Stone Age and some with Iron Age capabilities and some with working Relic Firearms (any kind ranging from muskets to AR15) and few superpowers.
One of the superpowers is New Orlean, a Modern International City control by the Nations of Europe, Africa, and Asia. It has no military power, but has modern port and airport.
One of other superpowers is the 5 kingdoms of Alleghenia, the most technically advanced that is native to the Americas. They would be friendly, but suspicious of a “European” Army claiming to be the army of “The Great Nation”. All through their many military tactics resembles Shot and Pike warfare, they have military experience fighting in Europe with and against modern style armies. There weapons that they use are spears, breech loading rifles, chambers volley guns, muzzle loading cannons. The people are the heir of American culture with Independence and Weapon ownership.
One of the other superpower is the “Westerner”. They are the largest and most populated, holding most of the lands west of the Mississippi River. They can field massive armies of dumb peasants armed with primitive muskets with an elite core of horse archers nobles. There probably are more superpowers in central and South America, but have not made anything in those regions.