May 1st celebrations go back as far as you care to look. Best known, it was a beginning-of-summer sort of pagan thing. Big one - lots of crazy stuff if you want to take a peek at it's history. It's general evolution was then towards a workers/serfs/peasants day.

Politics (socialism in particular, but plain old unionism too) usurped it, much like yule was usurped by Christianity. Just the typical way TPTB keep regular folk from having any sort of frenzied good time. (can't let us remind ourselves of our own personal freedom and power, and connection to each other and the earth)

Biggest holiday I know of that hasn't been commercialized, btw.