A bit of history, from the source above (I have added emphasis to a couple of lines I really liked)
The French had landed in Mexico (along with
Spanish and English troops) five months earlier on the pretext of collecting
Mexican debts from the newly elected government of democratic President (and
Indian) Benito Juarez. The English and Spanish quickly made deals and
left. The French, however, had different ideas.
Under Emperor Napoleon III, who detested the
United States, the French came to stay. They brought a Hapsburg prince
with them to rule the new Mexican empire. His name was Maximilian; his
wife, Carolota. Napoleon's French Army had not been defeated in 50 years,
and it invaded Mexico with the finest modern equipment and with a newly
reconstituted Foreign Legion. The French were not afraid of anyone,
especially since the United States was embroiled in its own Civil War.
The French Army left the port of Vera Cruz to
attack Mexico City to the west, as the French assumed that the Mexicans would
give up should their capital fall to the enemy -- as European countries
traditionally did. [ed.-- and as the French inexplicably did as recently as 1940]
Under the command of Texas-born General
Zaragosa, (and the cavalry under the command of Colonel Porfirio Diaz, later to
be Mexico's president and dictator), the Mexicans awaited. Brightly
dressed French Dragoons led the enemy columns. The Mexican Army was less
General Zaragosa ordered Colonel Diaz to take
his cavalry, the best in the world, out to the French flanks. In response,
the French did a most stupid thing; they sent their cavalry off to chase Diaz
and his men, who proceeded to butcher them. The remaining French
infantrymen charged the Mexican defenders through sloppy mud from a thunderstorm
and through hundreds of head of stampeding cattle stirred up by Indians armed
only with machetes.
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.
Union forces were then rushed to the
Texas/Mexican border under General Phil Sheridan, who made sure that the
Mexicans got all the weapons and ammunition they needed to expel the
French. American soldiers were discharged with their uniforms and rifles
if they promised to join the Mexican Army to fight the French. The
American Legion of Honor marched in the Victory Parade in Mexico, City.