Cinco de Mayo originally is a commemoration of a historic battle in Mexico's history, but the United States has since turned into something much bigger and a general celebration of the culture.
The history is an anniversary of Mexico's victory over France at the Battle of Puebla during the Franco-Mexican War in 1862.
The battle itself wasn't even a very large one in the grand scheme of things (the war would continue for a few more years after) but it helped boost the resistance effort and showed that the country was one to be potentially be on the lookout for.
