Contrary to what many believe, The 5th of May is not Mexican Independence Day! (If I hear this one more time...lol). Mexico declared its independence from Spain on the 15th of September, 1810.
So why do we celebrate this day? On May 5, 1862, 4,000 Mexican soldiers crushed the French and traitor Mexican army of 8,000 at Puebla, Mexico. After invasion by the French, the Mexicans won a great victory that kept Napoleon III from supplying the confederate rebels for another year (after non defeat in 50 years), allowing the United States to build one of the greatest armies the world had ever seen. This army smashed the Confederates at Gettysburg just 14 months after the battle of Puebla, essentially ending the Civil War. In gratitude for assistance by the Americans, thousands of Mexicans crossed the border after Pearl Harbor to join the U.S. Armed Forces.
Cinco de Mayo celebrates freedom and liberty, two ideals which Mexicans and Americans have fought shoulder to shoulder to protect, ever since the 5th of May, 1862.