Spanish attempts to reconquer Mexico
Mexican independence was officially achieved on September 27, 1821, under the Treaty of Córdoba. Spain did not recognize the treaties, arguing that the viceroy Juan O'Donojú had no authority to recognize the independence of any overseas province. This situation was dangerous to the newly acquired independent status of the nation, which had not yet been recognized by any of the European powers that could support it, and the threat of Spanish reconquest was a constant worry to the leaders of the nascent regime. On May 13, 1822 decrees were issued by the government to imprison anyone who conspired against Mexico's independence.
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.