Always honored at the Fifth of May, it's a [[AmericanHolidays celebration of Mexican culture]] in honor of a minor-but-significant battle victory of Mexico over an invading European force - okay, France - back in 1862, when the struggling Mexican nation was attempting to retain its republic status.
Ironically, Cinco de Mayo isn't a major celebration in Mexico itself: the holiday became much more important in the United States among Mexican-Americans as a point of cultural pride (very similar to St. Patrick's Day for the Irish). It's also mistaken by a lot of non-Mexicans - okay, Caucasian Americans - as Mexico's Independence Day (the real Mexican 4th of July is September 16th). There's an UrbanLegend that Cinco de Mayo really took off as a celebration when Chicano student groups at various California schools during TheSixties wanted to have a national pride day but couldn't use September 16th because it was at the start of school years, whereas May 5th came at the end of school years and easier to get people to join in.
And much like St. Patrick's Day, it's become accepted as a day for non-members of the ethnic group to indulge in the food (and beer!) of that ethnic group.
Tropes Associated with this holiday:
* UsefulNotes/TheAmericanCivilWar: was raging at the moment, which is why France hoped to conquer Mexico while the United States was unable to defend its MonroeDoctrine. Using the war debts from the UsefulNotes/MexicanAmericanWar as an excuse, Napoleon III sent an expeditionary force alongside Great Britain and Spain to force Mexico to pay up. When British and Spanish leaders figured out what Napoleon was up to, they settled with Mexico under amicable terms and refrained from the invasion.
* BadassBookworm: General Ignacio Zaragoza, who started out in life as a seminary student in the 1840s, but joined the forces in opposition to dictator Santa Anna in the 1850s and proved his worth leading a RagtagBunchOfMisfits to glory in battle. By 1862 he was serving as the Secretary of War in government, but resigned the post to lead the troops at the Battle of Puebla. Sadly, he died from typhoid soon after, unable to prevent the invading French from occupying Mexico one year later.
** BadassBoast: "The national arms have been covered with glory." - Zaragoza sending word of victory to President Juarez.
* CurbStompBattle: what Napoleon III was hoping for in trying to conquer Mexico. Zaragoza's victory proved that wrong. Napoleon III sent in more troops over the following year, while the Mexicans were able to organize an effective resistance during that year to prevent complete occupation. By 1866, with the United States finishing its war and massing on the border to enforce Mexico's independence, Napoleon was forced to pull his troops out.
* HeelFaceTurn: Britain and Spain, upon finding out that France wasn't just saber-rattling to get Mexico's attention, cut their own deal with Mexico over their debts and refused to help France invade.
* UsefulNotes/MexicanAmericanWar: part of the fallout from that war.
* MisaimedFandom: in a way. Most of Mexico itself doesn't celebrate Cinco de Mayo as a major holiday - outside of the Puebla region where the battle took place - but it's become a huge deal in the United States, especially advertised by beer companies and Mexican eateries.
** Other nations throughout the Caribbean celebrate it as well. It's celebrated in Australia with an annual festival, while in Japan the day is for celebrating American culture in general.
* VitriolicBestBuds: the United States, with Mexico. While the U.S. couldn't do much while embroiled in their own war, the Union government kept pressure on France to prevent a larger invasion, and when the Civil War ended by mid-1865 it immediately sent troops to the Texas/Mexican border and increased armaments and supplies to the Mexican government-in-exile. Realizing they were about to face the [[OhCrap largest organized]] - and ''battle-tested'' - standing army in the world at 500,000 U.S. troops (led by [[BloodKnight Philip Sheridan]] of all generals!) if they didn't leave per the Monroe Doctrine, the French occupiers quit their attempt at empire, allowing Mexico to rebuild its republic.