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.
Puebla
Cinco de Mayo—or the fifth of May—is a holiday that celebrates the date of the Mexican army's 1862 victory over France at the Battle of Puebla during the Franco-Mexican War (1861-1867). A relatively minor holiday in Mexico, in the United States Cinco de Mayo has evolved into a commemoration of Mexican culture and heritage, particularly in areas with large Mexican-American populations. 
Many Americans mistakenly believe that Cinco de Mayo (“May 5th”) is the Mexican equivalent of the United States’ Fourth of July holiday — a date marking the official casting off of colonial rule via the announcement of a new independent country. However, the Mexican version of Independence Day is celebrated on September 16, for it was on that date in 1810 that the commencement of the war for Mexican independence from Spanish rule was pronounced in the small town of Dolores by Miguel Hidalgo y Costilla (an event now referred to as the “Grito de Dolores” — “Cry of Dolores” — or “El Grito de la Independencia”).