Cinco de Mayo is an unofficial holiday in Mexico which commemorates the defeat of French forces by the Mexican Army led by Gen. Ignacio Zaragoza. The battle took place in the outskirts of Puebla, Mexico on May 5, 1862, hence its formal name of "Battle of Puebla," and its colloquial name of "Cinco de Mayo." http://www.mexonline.com/cinco-de-mayo.htm
Militarily, the battle is defined as a tactical victory for the Mexican Army, but in a broader context it was insignificant in terms of preventing the implantation of French rule over Mexico by France under the rule of Napoleon III, through a newly placed monarch for Mexico, Emperor Maximilian I. The new imperial regime had support within Mexico, mainly by the upper and merchant classes coupled with the clergy, but resistance was mounted by the then elected president of Mexico, Benito Juarez, who retained the loyalty of many army officers and units.
The catalyst which brought about a French presence in Mexico, was Mexico's decision to suspend debt payments to foreign creditors. Great Britain and Spain resolved the issue through diplomatic channels, but France utilized it as an opportunity to gain dominion over Mexico, taking advantage of the fact that the United States was embroiled in a Civil War and therefore unable, or unwilling to act upon its established Monroe Doctrine against European implantation in the Americas.
It was within this context, that French forces entered into the Battle of Puebla on the road to Mexico City. The Mexican forces numbered approximately 4,000, while the French numbered 8,000. With the tactical defeat, which was the first for France involving a "battle-level" event since the Battle of Waterloo nearly 47 years earlier, the French retreated back towards the Mexican Gulf coast to regroup. Eventually, the city of Puebla was taken by the French a little over a year later on May 17, 1863, with Mexico City capitulating on May 30, 1863 opening the road for Emperor Maximilian to arrive in 1864 and claim his newly established throne.http://www.mexonline.com/cinco-de-mayo.htm
Currently, the date has only passive observance within the country of Mexico itself, but has taken on cultural significance to many people of Mexican descent residing in other countries, especially the United States, were the day is marked more as a cultural celebration, akin to St. Patrick's Day for Irish pride, without much correlation to its actual historical context.http://news.nationalgeographic.com/news/2006/05/0505_060505_cinco_de_mayo.html Many people outside of Mexico erroneously associate the date and the celebration as Mexican Independence day, which is actually celebrated on September 16.http://news.nationalgeographic.com/news/2006/05/0505_060505_cinco_de_mayo.html