Cinco de Mayo (Spanish for 'fifth of May') is a Mexican holiday that celebrates the Mexican Army's victory over a much stronger and larger French army at the Battle of Puebla on May 5, 1862. It is celebrated mainly in the Mexican state of Puebla and in the United States because of the battle's significance in the outcome of the American Civil War.
Emperor Napoleon III of France saw the American Civil War as an opportunity to gain influence and power in Central and North America. Historians believe his plan was to establish a base in Mexico and then provide support to the southern Confederacy. The defeat of the French army, which delayed much needed support to the Confederacy, allowed the Union army to amass the necessary forces to eventually turn the tide of the war.
The holiday is now observed as a celebration of Mexican American heritage.