Today, the 5th of May, celebrates the Mexican victory over the French army at the “Batalla da Puebla.” The celebration of Cinco de Mayo first started in 1862.
According to Wikipedia:
In the United States, Cinco de Mayo has taken on a significance beyond that in Mexico. The date is perhaps best recognized in the United States as a date to celebrate the culture and experiences of Americans of Mexican ancestry, much as St. Patrick’s Day, Oktoberfest, and the Chinese New Year are used to celebrate those of Irish, German, and Chinese ancestry, respectively. Similar to those holidays, Cinco de Mayo is observed by many Americans regardless of ethnic origin. …Commercial interests in the United States have capitalized on the celebration, advertising Mexican products and services, with an emphasis on beverages, foods, and music.