Third Treaty of San Ildefonso

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The Third Treaty of San Ildefonso (formally titled the Preliminary and Secret Treaty between the French Republic and His Catholic Majesty the King of Spain, Concerning the Aggrandizement of His Royal Highness the Infant Duke of Parma in Italy and the Retrocession of Louisiana) was a secretly negotiated treaty between France and Spain in which Spain returned the colonial territory of Louisiana to France. The treaty was concluded on October 1, 1800 between Louis Alexandre Berthier representing France and Don Mariano Luis de Urquijo for Spain. The treaty was negotiated under some duress, as Spain was under pressure from Napoleon. The terms of the treaty did not specify the boundaries of the territory being returned, which later became a point of contention between Spain and the United States after the Louisiana Purchase in 1803, in which France sold its territory to the United States. This treaty also affirmed the earlier Treaty of Alliance signed at San Ildefonso on August 19, 1796. That treaty is sometimes also referred to as the Treaty of San Ildefonso.