What happened in 1803 that changed the united states

The Louisiana purchase i believe is the answer you're looking for

The Supreme Court of the United States is the highest federal court of the United States. Established pursuant to Article III of the United States Constitution in 1789, it has ultimate (and largely discretionary) appellate jurisdiction over all federal courts and over state court cases involving issues of federal law, plus original jurisdiction over a small range of cases. In the legal system of the United States, the Supreme Court is the final interpreter of federal constitutional law, although it may only act within the context of a case in which it has jurisdiction. The answer is  Louisiana purchase 

Americans agreed to the settlement terms established by the mexican government.

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