Holiday is a lot bigger here than Mexico
As Cinco de Mayo grows in importance as a Hispanic holiday in the U.S., many people mistakenly think it's Mexico's independence day when it really commemorates a small military victory.
On May fifth, 1862, an ill-equipped Mexican army defeated French troops. Mexico's real independence day is September 16th. Few Americans know about the battle, but plenty can name a Mexican beer to celebrate Cinco de Mayo with. Beer and liquor companies have been heavily promoting it in recent years.
On this side of the border, Cinco de Mayo has evolved into a "uniquely American phenomenon" similar to St. Patrick's Day -- more U.S. enthusiasm for it than in the home country.