Cinco de Mayo commemorates the day that Mexican troops defeated Napoleon III's army on May 5, 1862, in the Battle of Puebla, which became a symbol of Mexican unity and patriotism.
Some people mistakenly think Cinco de Mayo is Mexico's Independence Day, but the country actually declared its independence on September 16, 1810. Maintaining its independence was not easy for Mexico, and during this period it accumulated heavy debts to several nations, including France, England and Spain.
In 1861, with many different political groups struggling to gain power, Mexico was nearly bankrupt, so President Benito Juarez issued a moratorium on all foreign debt payments for a period of two years, after which payments would resume. England, Spain and France refused to allow this, and instead invaded Mexico to get repayment in whatever way they could. The English and Spanish eventually withdrew, but not the French.
In 1862, the well-trained army of Napoleon III advanced on Puebla, where a poorly equipped Mexican army was led by General Ignacio Zaragoza. Though outnumbered, Zaragoza's troops defeated the French, considered the most powerful army in the world at that time. It was a great boost to Mexican morale and pride. One year later the French returned with more troops and took Mexico City, installing Emperor Maximilian as Mexico's monarch. Although he ruled for four years before being executed in 1867, when President Juarez regained power, the Battle of Puebla is remembered as the day that Mexico began to hold its head up high.