This is according to new research by Professor David Hayes-Bautista says the holiday owes as much to the United States as it does to Mexico. In a new book, he claims that the holiday was created by Latinos in the West during the Civil War. He found this while poring over newspapers of the 1800s while he was working on another research project.
So what's the story of Cinco de Mayo? What Prof. Hayes-Bautista found was that US Latinos during the Civil War were sympathetic towards the Union, because they believed in freedom against slavery. At around the same time, the French army, who supported the Confederates, was trying to conquer Mexico and impose a monarchy. On a May 5th, the Mexican Army had a great victory against the French. Newspapers in California and Oregon used this victory as a rallying cry and a sign that their side was going to win both wars - against the French and against Confederates.
The general sentiment among Latinos in the US was more about the "good" guys beating the "bad" guys, rather than the French army suffering defeat. Their victory was a rallying cry for so-called patriotic Mexican juntas, who would celebrate monthly parades and give speeches every Cinco the Mayo. The years of 1862 to 1867 were the formative years in which Cinco de Mayo was cemented in public memory.
The truth is, Prof. Hayes-Bautista says, that Cinco the Mayo has now joined the ranks of other big commercial holidays, where big beer companies take advantage of a day to sell all the imported drink that they can manage to get out to the public. But now you know, the holiday you're celebrating is anything but imported, and it hasn't just been brought to the US recently. Cinco de Mayo is as American as hardshell tacos.