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Your challenge if you choose to accept it is to make the United States of America formally surrender to another country. You can use any pod as long as it is not before 1900. No white peace or simple ceasefire is allowed. The USA must come out the clear losing side the same way Imperial Germany or Japan in WWII surrendered for example.
You have over 100 years to work with so this gives plenty of opportunities for creativity. America might be too strong to be beaten by one power but a massive coalition is another story.