Mexican War of Independence
The Mexican War of Independence () was an armed conflict, and the culmination of a political and social process which ended the rule of Spain in 1821 in the territory of New Spain. The war had its antecedent in Napoleon's French invasion of Spain in 1808; it extended from the Cry of Dolores by Father Miguel Hidalgo y Costilla on September 16, 1810, to the entrance of the Army of the Three Guarantees led by Agustín de Iturbide to Mexico City on September 27, 1821. September 16 is celebrated as Mexican Independence Day.
Mexico–United States relations
U.S.–Mexico relations grew out of the earlier relations between the fledgling nation of the United States and the Spanish Empire and its viceroyalty of New Spain. Modern Mexico formed the core area of the Viceroyalty of New Spain at the time the United States gained independence from Great Britain in the American Revolutionary War (1775–1783). Spain had served as an ally to the American colonists in that war.