A look at Cinco de Mayo, and the effect it had on the war raging in the USA.
Hayes Bautista says California Latinos were ardent Union supporters. When their home countries won independence from Spain, they had unilaterally abolished slavery and established citizenship for non-whites. Now living in California, a free state, they saw the pro-slavery Confederacy as an existential threat. When reports reached Los Angeles of Zaragoza’s victory against the French, Latinos made the Civil War connection immediately.
“In 1862, things weren’t going well for the Union in the Civil War, but here in Puebla was a clear-cut victory that completely threw the French timetable off,” says Hayes-Bautista. “The news reports just electrified Latinos and jolted them to a whole new level of organization and activity.”
Source: How Cinco de Mayo Helped Prevent a Confederate Victory in the Civil War