While many assume that Cinco de Mayo is somehow equivalent to the Fourth of July as a day of independence, there is a great deal of history to the day that is misunderstood - especially in the U.S.
Cinco de Mayo commemorates the victory of the Mexican militia over the French army at The Battle Of Puebla in 1862. Mexico's independence day is, in fact, September 16 and occured some 41 years before. It is primarily a regional holiday celebrated in the Mexican state capital city of Puebla, with some limited recognition in other parts of Mexico and in U.S. cities with a significant Mexican population.
So why were they fighting the French when they had previously won their independence from Spain? After years of bloody conflict, including the Mexican-American War (1846-1848), the Mexican Civil War of 1858, and winning independence from Spain in the first place, the national economy was ruined, and Mexico had significant debt to countries such as England, Spain and, yes, France.
Eager to expand their empire, and demanding repayment, France invaded at the gulf coast of Mexico and began to march toward Mexico City with the idea of installing one of their own as the Mexican ruler. England and Spain, realizing what France was about to do, withdrew their support from Mexico. As for the U.S., President Abraham Lincoln was sympathetic to Mexico's cause, but the U.S. was involved in its own Civil War at the time and was unable to provide any direct assistance.
At Puebla, the French army encountered a smaller, poorly armed militia estimated at 4,500 men lead by Mexican General Ignacio Zaragoza Seguin. At that battle the band was able to stop and defeat a well-outfitted French army of 6,500 soldiers, which stopped the invasion of the country.
Mexico's battles were far from over, as the French leaders did not take their defeat at Puebla kindly, but the day of that victory is still celebrated as a day of national unity, honoring the few brave forces that stopped the initial invasion despite being outnumbered.
Celebrating Cinco de Mayo has become increasingly popular along the U.S.-Mexico border and in parts of the U.S. that have a high population of people with a Mexican heritage. The holiday is a celebration of Mexican culture, food, music, beverage and customs unique to Mexico.
So, yes. Raise a margarita in celebration of Cinco de Mayo - but remember to celebrate not only the tasty beverage at hand, but the history of strength and defiance the day marks for our neighboring nation.