Happy Cinco de Mayo, amigos!
In the latter part of 1861, the French invaded Mexico, causing President Juarez to retreat to Mexico City. Over the course of several months, the French followed the president, but the Mexicans met them with strong resistance.
The undefeated French army, consisting of around 8,000 well-armed soldiers using superior technology, attacked a poorly equipped Mexican army, which had only around 4,000 soldiers. After much bloody fighting and against all odds, the Mexican army achieved a decisive victory over the French on May 5, 1862.
Consequently, these hardy Mexican fighters prevented the French from getting involved in the U.S. Civil War, significantly affecting the outcome of that war.
History is fun, right?