On Saturday, many Americans are celebrating a holiday they likely know almost nothing about.

I’m speaking, of course, of Cinco de Mayo, which is Spanish for May 5. Although the day is supposed to celebrate Mexican heritage, it has become Americanized — that is, hijacked into another excuse to party, eat, and drink, all while getting sweet discounts at some restaurants. (It is so Americanized, in fact, that it’s actually celebrated more in the US than in Mexico.)

The origins of the holiday go back to, as one would expect, Mexican history. But Cinco de Mayo is not Mexican Independence Day (September 16), as many people believe. It is, instead, a day commemorating an important battle after Mexican independence.

These details might not seem crucial to your partying needs. But the origins are an important part of the Mexican heritage many Americans are supposed to be celebrating today — and give some insight into why this uniquely Mexican-American holiday is now celebrated in the US.

What is Cinco de Mayo? Its origins go back to a 19th-century battle.

Let’s be clear: Mexican Independence Day is September 16, 1810, the beginning of Mexico’s revolution against Spain. It is not Cinco de Mayo.

Cinco de Mayo does, however, have roots in Mexico’s struggle with another European power.

In 1861, Mexican President Benito Juárez declared that his country couldn’t afford to pay its debts. This, as one would expect, did not please the countries that had made loans to Mexico — and Britain, Spain, and France sent naval forces to Mexico to secure their debts.

Britain and Spain managed to negotiate the issue peacefully. But the French, ruled by Napoleon III, decided to invade, taking over the country and setting up a monarchy led by an Austrian archduke.

But before the French managed to take over the country for several years, Cinco de Mayo gave Mexicans a glimmer of hope: When the French approached the town of Puebla on May 5, 1862, their army lost to a badly outnumbered and out-armed group of Mexican soldiers.

The Mexican victory was short-lived, and France eventually advanced to the nation’s capital and took over. But the win still turned into a symbol of Mexican resistance, helping sustain an independence movement that would go on for the next few years.

Driven by the spirit of Cinco de Mayo and with American support, Mexicans eventually — in 1867 — toppled the French-installed government and put Juárez back in power.

Over time, Cinco de Mayo became an American holiday

So how did Cinco de Mayo go from celebrating a struggle for Mexican liberation to a US holiday?

It goes back to the US and Mexico’s close ties — linked by proximity, a struggle against European imperialism for independence, trade, and immigration. (There’s also the US’s imperialism in Mexico.)

These close ties were also real in 1862, the year of Cinco de Mayo and second year of the American Civil War. The two events were tied, as Brian Greene reported for US News and World Report:

As the French were making war with Mexico, the American Confederacy was courting Napoleon’s help in its conflict with the United States. At the time of the Battle of Puebla, the Confederacy had strung together impressive victories over the Union forces. According to some historians, the French, who made war with Mexico on the pretext of collecting debt, planned to use Mexico as a “base” from which they could help the Confederacy defeat the North, and the Mexican victory at Puebla made the French pause long enough for the Union army to grow stronger and gain momentum. Had the French won at Puebla, some contend, the outcome of the American Civil War could have been much different, as the French and Confederates together could have taken control of the continent from the Mason Dixon line to Guatemela [sic], installing an oligarchical, slave-holding government.

This link between the victory in Puebla and the Civil War drove Mexican Americans in California to celebrate the holiday as part of the cause to abolish slavery. As David Hayes-Bautista, author of El Cinco de Mayo: An American Tradition, told the Associated Press, Hispanic Americans in the western US even celebrated Cinco de Mayo in parades while dressed in Civil War uniforms.

Over time, Mexican Americans’ festivities transformed into a broader celebration of their Mexican heritage, particularly as Mexican Americans adopted Cinco de Mayo as a rallying cry in their struggle for civil rights in the 1970s. (The civil rights link has stuck — at times leading to protests and riots. On May 5, 1991, for example, the police shooting of a Salvadoran man led to three days of riots in the Mount Pleasant neighborhood of Washington, DC.)

Eventually, the celebrations became so prominent that white Americans began to take part in the holiday as well. With that, major companies began getting involved to make Cinco de Mayo into a profitable venture.

But as the holiday grew broader, so did its focus — and with that, its true origins were mostly lost.

Cinco de Mayo has turned into another reason to booze up

None of this history has any bearing on how most Americans take part in Cinco de Mayo. Insofar as the holiday’s Mexican origins color how most Americans celebrate the day, it mostly just changes the kind of alcohol and food people consume as they party.

This, of course, isn’t exclusive to Cinco de Mayo. It’s happened with St. Patrick’s Day, which went from celebrating the top patron saint of Ireland to essentially celebrating alcohol, America’s second deadliest drug. It’s something we’ve seen with holidays like Halloween, Thanksgiving, and Christmas, which have over time transformed more into reasons to buy a bunch of stuff — candy, food, booze, gifts, and so on.

Similarly, the food and alcohol industries have transformed Cinco de Mayo into a huge day for advertising and sales. According to CNN, in 2014 the Friday closest to Cinco de Mayo was the biggest non-winter drinking day of the year.

This is just what capitalism does to holidays in America. And, hey, it can be pretty fun. But since booze is so dangerous (linked to 88,000 deaths each year), it’s also a public health and safety hazard — to the point that state agencies warn people to take it easy on the drinking during holidays like Cinco de Mayo. And the corporate takeover of Cinco de Mayo has also by and large diluted the holiday’s origins.

But at the very least, knowing the origins of Cinco de Mayo will give you something to talk about with strangers as you down fajitas and margaritas on Friday.