The authors suggest that the defeat of the French in Mexico may have also helped the Union in the American Civil War. It is known that Napoleon III wanted to recognize the Confederacy as an independent nation, and some historians believe that had he triumphed in Mexico, his next step would have been to head toward the U. S. border in order to help the Confederate army (link).
When the battle was over, many French were killed or wounded and their cavalry was being chased by Diaz' superb horsemen miles away. The Mexicans had won a great victory that kept Napoleon III from supplying the confederate rebels for another year, allowing the United States to build the greatest army the world had ever seen. This grand army smashed the Confederates at Gettysburg just 14 months after the battle of Puebla, essentially ending the Civil War.
So there's a possibility that those Mexican peasants may have contributed their little part to preserving the Union and ending slavery in the American South.
Recently there has been a lot of conflict between Latinos and Blacks in Los Angeles. Today, let's remember the ways that our respective communities have helped each other in the past and celebrate Cinco de Mayo together.