It's a common misconception that Cinco de Mayo is the celebration of Mexican Independence day. The May 5th celebration is actually the marking of a win by a small faction of the Mexican Army over the French during the French-Mexican war.
A Cinco de Mayo celebration in Washington, D.C.
In reality, Americans actually do have a cause to celebrate and commemorate the Texan-born Mexican general, his ragtag battalion of enlisted volunteer troops and their unlikely defeat over the French Army at the battle of Puebla on May 5th, 1862. Despite being outnumbered 3-1, the Mexicans obliterated the French, forcing a retreat after the French sustained over 500 casualties, compared to the Mexican's mere 100 deaths in the battle.
What many people might not know was that the French were planning a lot more than just a one-off takeover of the small Mexican city of Puebla. Along with this mounted offensive, Napoleon and his Army were planning to exchange their superior and advanced artillery with the American Confederate Army in exchange for southern cotton; a commodity that was growing quite sparse across the pond in Europe.
Had the French won the battle of Puebla and made that deal with the Confederates, our Civil War most-certainly would have turned out quite differently. At the time France was known to have some of the most technologically advanced and deadly firepower in the world. And if they had supplied their weapons to the Confederates, the Union Army's fight would have become exponentially more difficult, causing more deaths and perhaps even resulting in a Union defeat; an outcome that would have changed the course of US history.
So be sure to have a celebratory margarita this Cinco de Mayo and when someone asks you why we Americans tend to celebrate this holiday in more numbers and with more gusto than our neighbors to the south, just smile and pour one out for the warriors that won the Battle of Puebla and saved us from a significantly bloodier and potentially-disastrous end to the American Civil War.