Cinco de Mayo by David Hayes-Bautista is an historical explanation of why Cinco de Mayo is celebrated in the United States, but it is almost unknown as a holiday in Mexico.
The Mexicanos in California had gone from being a part of Mexico to a part of the United States. Although there were many guarantees of rights in the treaty between the United States and Mexico, they were frequently not observed after California became part of the U.S. Their lot had changed, and they felt very much threatened during the time of the U.S. Civil War. The Confederacy professed both slavery and white supremacy; if the Confederacy won the war, slavery could be extended to the Pacific. The French intervention in Mexico threatened democracy there. Both wars were going badly from the perspective of democracy and equality. The Battle of Puebla in Mexico was the first hopeful sign of a turn toward hope.
Since then Cinco de Mayo has been a sign of hope, been a patriotic U.S. holiday, a rallying point in the Chicano movement, and commercialized. “And with mighty hand and outstretched arm…..”now been theologized……Ooops, I made that one up.
I highly recommend this book. It explains a lot and shows how an idea can be used and celebrated in different ways over the decades. It’s available in hardcover, paperback, and Kindle.