Like most national celebrations and holidays, Cinco de Mayo started with honest intent, connected to some important historical event, but was eventually commercialized into a booze-filled party absorbed by outside cultures. While a majority of people explain Cinco de Mayo as "the Mexican Fourth of July" in-between margarita sips, this isn't correct either. As David E Hayes-Bautista, Director of the Center for the Study of Latino Health and Culture at the School of Medicine at UCLA, told Time, "Cinco de Mayo is part of the Latino experience of the American Civil War."
In the early 1860s, Mexico had fallen in immense debt to France. That situation led Napoleon III, who had flirted with supporting the confederacy, to send troops to not only overtake Mexico City, but also to help form a Confederate-friendly country that would neighbor the South.
"The French army was about four days from Mexico City when they had to go through the town of Puebla, and as it happened, they didn't make it," Hayes-Bautista says. In a David-and-Goliath style triumph, the smaller and less-equipped Mexican army held off French troops in the Battle of Puebla, on the fifth of May of 1862. (The French army returned the following year and won, but the initial Mexican victory was still impressive.)
Head over to Time to read more.