Cinco de Mayo
Cinco de Mayo, the 5th of May in Spanish, is a Mexican regional holiday that, within Mexico, is celebrated primarily in the state of Puebla and the federal district but is also observed in other parts of Mexico. It has taken on greater status as a celebration of Mexican heritage in areas where the Mexican diaspora live, and because of this people sometimes erroneously assume that it marks the date of Mexican independence. Cinco de Mayo actually commemorates a victory of Mexican forces over French forces on May 5th, 1862. Although the French recovered and eventually occupied Mexico, they were finally routed in 1867.
The Battle of Puebla
For more information, see the full article: Battle of Puebla
In July of 1861, Mexico's president Benito Juarez announced that all payments would be suspended on the substantial debt that the Mexican government owed to Spain, France, and England. This suspension was to be effective for at least two years. The lending nations were duly alarmed and dispatched soldiers to the port of Veracruz. The Mexican government negotiated a withdrawal of the Spanish and English forces, but French troops remained at Veracruz from where they were ordered to march on Mexico City in 1862.
The French encountered significant resistance at Puebla. There, Mexican General Ignacio Zaragoza held off three successive attacks by the French army, which was composed of some 6,000 cavalry and infantry, with 2,000 ill-equipped and poorly trained soldiers who were supported by the local populace. The last of the three battles took place on May 5th.