The most common thing people get wrong: Cinco de Mayo is not Mexican Independence Day. That holiday is September 16. Here's the short version of what today actually marks.
The Battle of Puebla, 1862
On May 5, 1862, a small, under-equipped Mexican army under General Ignacio Zaragoza defeated a much larger French force at the city of Puebla, southeast of Mexico City. The French were trying to install a monarchy in Mexico under Maximilian of Austria. They eventually succeeded for a few years — Puebla wasn't the end of the war — but the unexpected victory at Puebla became a national symbol of resistance and fueled a movement that ran the French out of Mexico by 1867.
Why it's bigger in the U.S. than in Mexico
In Mexico, Cinco de Mayo is a regional holiday — observed mostly in the state of Puebla itself, with battle reenactments and parades. It is not a federal holiday. The U.S. version of the holiday took shape separately. Mexican-American communities in California began commemorating the date as early as 1863 as a political and cultural rallying point, and Chicano activists revived it during the civil rights movement in the 1960s. The mass-market version most Americans know today — tacos, margaritas, and tequila brand promotions — emerged later, mostly as a 1980s marketing build by beer and spirits companies.
What's actually traditional
If you wanted to eat the foods that Puebla actually associates with the day, you'd be eating mole poblano, chalupas, and lamb barbacoa — not nachos and frozen margaritas. That's part of why Jacinta de México's Sabores de Puebla menu (above) is the most historically grounded option in the area tonight.