Corporate advertisers treat Cinco de Mayo as the de facto Mexican Day, if not Latino Day, in this country. In 1998, the U.S. Postal Service issued a Cinco de Mayo stamp featuring two folklórico dancers. In 2005, Congress passed a resolution making the day an official national holiday to celebrate Mexican-American heritage. And it’s customary for presidents to celebrate Cinco de Mayo on the White House lawn with margaritas flowing, mariachi music playing and dancers in brightly colored traditional costumes.

Don’t they all know that Mexican Independence Day is actually Sept. 16?

Growing up in rural Zacatecas, Mexico, in the early 1970s, holidays and festivities were big, community-building affairs. I attended fiestas with tamborazostyle band music, rodeos with charros showing off their roping and riding skills and the religious procession honoring the town’s patron saint. What I remember most was El Grito, the traditional cry of “Viva Mexico!” to commemorate Mexico’s independence from Spain on Sept. 16. Like Christmas, the holiday is celebrated on the eve of the big day, and the day itself. But I have no memory of Cinco de Mayo, at least not before migrating to the United States.

It was in my elementary school’s bilingual education classroom in Ventura, Calif., that I first learned about the holiday, which had been incorporated into lesson plans and school assemblies on cultural diversity. In high schools at the time, Mexican American students began organizing their own Cinco de Mayo celebrations to show off their cultural pride and make a public claim of belonging.

Cinco de Mayo is indeed a holiday in Mexico, but a lesser holiday not associated with any particular form of revelry. It’s the anniversary of the famous battle of Puebla, in which Mexican liberal forces defeated an occupying French army and its Mexican conservative allies during one of Mexico’s serial 19th century civil wars. By helping to impose an unemployed Hapsburg prince as Mexican emperor, the French were hoping to gain a new beachhead in the Americas while the United States was distracted with its own epic civil war.

So why was this, of all Mexican holidays, the one to stand out on this side of the border, in the face of ostensibly stronger contenders? One theory is that it would have been awkward for Mexicans in the United States to be too eager to celebrate the official independence day of another country. The generations of Mexican immigrants who came to America weren’t necessarily on the best terms with the authoritarian Mexican governments of yesteryear, and weren’t keen to celebrate. Better to focus on a different holiday altogether: Cinco de Mayo.

There is an additional, more prosaic, explanation for Cinco de Mayo’s stature north of the border: May is a more convenient time for migrant farmworkers to celebrate.

My doctoral research on the holiday’s popularity led me to Corona, Calif. The town once known as the “Lemon Capital of the World” was one of the earliest to celebrate Cinco de Mayo in the United States. Mexican workers made up the majority of the labor force working in the 2,000 acres of lemon groves, 11 packing houses and lemon-processing plant in 1930s Corona. Lemons were grown in winter months but harvested in springtime, just in time for Cinco de Mayo. The timing of the lemon harvest meant people would welcome a reason to rest and celebrate and have a little more disposable income than usual, not to mention ideal weather. When May 5 fell on a weekday, employers paid workers early, and students were dismissed from class early to attend the festivities.

Corona’s Cinco de Mayo celebration still strives to be local, intimate and inclusive. The morning parade continues to feature local heroes and role models as grand marshals — the mother of a World War II hero killed in action or a Latina superior court judge — rather than outside celebrities. The town limits sponsors to local businesses and nonprofit organizations. Proceeds from the celebration provide college scholarships to local Latino high school students.

There is no beer or alcohol sponsorship of Corona’s Cinco de Mayo, though you can’t talk about the popularity of the holiday everywhere else without talking about the other Corona. The corporate marketplace started pushing Cinco de Mayo as a day-long happy hour for downing cervezas and margaritas when it recognized the demographic growth of the Latino population in the 1980s. Corporations thought that advertising, sponsorship and promotion of Cinco de Mayo events would enable them to tap into that young consumer market. Beer and alcohol companies led the charge by spending millions on marketing the holiday. Corona Extra (the beer — no relation to the town) alone spent $91 million in 2013 on advertising around the holiday in both Spanish and English, calling itself “the original party beer of Cinco de Mayo.”

I don’t think that means there were kegs on the battlefield in Puebla, but it’s an amusing image. So go have a drink on Cinco de Mayo. But when you do, take a moment to reflect on the evolution of this holiday that commemorates the Americanization of a Mexican diaspora eager to assert its own identity — and, increasingly, the Mexicanization of mainstream U.S. culture as well. ¡Salud!

This article was written in partnership with Zocalo Public Square.