Here's what Cinco de Mayo has become in the U.S.: a celebration of all things Mexican, from mariachi music to sombreros, marked by schools, politicians and companies selling everything from beans to beer.

And here's what Cinco de Mayo is not, despite all the signs in bar windows inviting revelers to drink: It's not Mexico's Independence Day, and it's barely marked in Mexico, except in the state of Puebla, where the holiday is rooted in a complicated and short-lived 1862 military victory over the French.

But don't let that spoil the party.

In Houston today, ballet folklorico dancers will ring in Cinco de Mayo by stomping to traditional Mexican music in a city park. New York City will close parts of Spanish Harlem and Queens for street fairs as Mexican flags flap from apartment fire escapes and car antennas.

Albuquerque honors the day with a Mariachi concert and free cab rides for those who show their love for Mexico with a little too much Dos Equis XX or tequila. Even West Des Moines, Iowa, has an all-day festival with Mexican food, artwork and live music.

The holiday has spread from the American Southwest, even though most are unaware of its original ties to the U.S. Civil War, abolition and promotion of civil rights for blacks.

Often mistaken for Mexican Independence Day (that's Sept. 16), Cinco de Mayo commemorates the 1862 Battle of Puebla between the victorious ragtag army of largely Mexican Indian soldiers against the invading French forces of Napoleon III. Mexican Americans, during the Chicano Movement of the 1970s, adopted the holiday for its David vs. Goliath storyline as motivation for civil rights struggles in Texas and California.

Over the years, the holiday has been adopted by beer companies as a way to penetrate the growing Latino market, even as the historical origins of the holiday remain largely forgotten.

Roots in Gold Rush

David Hayes-Bautista, a professor of medicine and health services at UCLA and author of the newly released "El Cinco de Mayo: An American Tradition," said the holiday's history in the U.S. goes back to the Gold Rush when thousands of immigrants from Mexico, Central and South America came to California during the Civil War.

According to Spanish-language newspapers at the time, this first group of multinational Latinos on U.S. soil identified with the Union Army's fight against the Confederacy and often wrote pieces about the evils of slavery. Hayes-Bautista said these Latino immigrants were concerned about the Union's lack of progress and Napoleon III's interests in helping the South.

"It wasn't until the news came about the Battle of Puebla that they got the good news they wanted," said Hayes-Bautista. "Since Napoleon III was linked to the Confederacy, they saw the victory as the first sign that their side could win."

They didn't, of course, at least not for a few years. French forces took over Mexico after the Battle of Puebla, and installed Habsburg Archduke Maximilian as Emperor of Mexico. He was captured by Mexican forces five years later and put to death.

But in the years that followed, Latinos in California and the U.S. Northwest celebrated Cinco de Mayo with parades of people dressed in Civil War uniforms and gave speeches about the significance of the Battle of Puebla in the larger struggle for abolition, said Hayes-Bautista.

The Cinco de Mayo-Civil War link remained until the Mexican Revolution, which sparked another wave of Mexican immigration to the U.S. Those immigrants had no connection to Cinco de Mayo — except that U.S. Latinos celebrated it.

"That's when it became about David vs. Goliath, Indians beating a European force, and it took on a new meaning," said Hayes-Bautista. "The Civil War ties disappeared."

The date received another jolt during World War II during the U.S. government's "Good Neighborhood Policy" aimed at building good relationships with Mexico and during the Chicano Movement, when Mexican American activists adopted the day to reinforce civil rights demands. Two police beatings of Cinco de Mayo revelers — one in Houston in 1978 and the other in Washington DC in 1991 — resulted in riots and sparked protests and calls for reforms from Latino advocates.

Spread from Southwest

The holiday spread outside of the American Southwest as more Latinos moved to new areas around the country. Alyssa Gutierrez, 35, a teacher who is originally from Robstown, Texas but now lives in New York's Harlem neighborhood, said Cinco de Mayo was barely noticed when she moved to New York in 1998. "Now there are Mexican restaurants on almost every block and all do something on Cinco de Mayo, usually around a boxing match," said Gutierrez.

Jody Agius Vallejo, a sociology professor at the University of Southern California and author of "Barrios to Burbs: The Making of the Mexican-American Middle Class," said Cinco de Mayo is now used by assimilated Mexican Americans as an easy way for them to showcase their ethnic identity.

"It's very similar to how Irish-Americans celebrate St. Patrick's Day," said Vallejo. "One way they can honor their ethnicity is to celebrate this day, even when most don't know why."

But not all buy in. "To others," she added, "this holiday is kind of viewed as a joke because they feel it's their culture that is being appropriated and exploited."

Hayes-Bautista said because the theme and focus around Cinco de Mayo has transformed a number of times, it won't be surprising if it changes again.

"No one has owned Cinco de Mayo," said Hayes-Bautista. "And no one ever will."