America's Napoleonic Legal Island

Louisiana is the only state in the United States that bases its civil law on the Napoleonic Code, a legal framework inherited from France and Spain rather than the English common law that governs every other state. This means Louisiana handles property, family, and contract disputes differently than the rest of the country. When Louisiana was purchased by the United States in 1803, its residents successfully lobbied to keep their existing legal traditions, creating a legal island that persists to this day and requires Louisiana lawyers to master an entirely separate body of law.

Source: Wikipedia