Cinco de Mayo marks a battle near Puebla in which a 4,000 man Mexican army defeated an 8,000 man French army. The French army at the time was considered the best in the world. Big day for Mexicans. But a year later the French conquered the Mexicans and established Maximilian as the emperor of Mexico.
However, he didn't last long either. Three years later the Mexicans, with increased support from the United States, overthrew and executed Maximilian and drove the French out of Mexico.
For some reason, Cinco de Mayo caught on as a day of celebration. But except for the area around Puebla and beach resorts that cater to Americans, not in Mexico. No, the holiday is celebrated widely in the United States, predominately by non-Mexicans. Go figure.
So . . . what to do? That's easy. Margaritas, Dos Equis cerveza (beer), tacos, enchiladas, and perhaps some mariachi music! Viva Mexico!