May Day, as an international workers" celebration, dates back to what 1886 event?

More Questions:

In 1990, what did the World Health Organization officially remove from its list of "mental illnesses"?

Which country traditionally gives London's Trafalgar Square its Christmas tree?

Which Old Master signed his paintings with his full Cretan name, Doménikos Theotokópoulos?

What was the last album recorded by The Beatles?

From what language did English borrow the word "zero"?

The US shares a border with how many countries?

The city of New Orleans is located in which state?

What is at an average distance of 238,857 miles from the Earth?

What instrument was Big Band leader Bennie Goodman most associated with?

Which song became synonymous with "The Bridge on the River Kwai"?

What did Dorothy's house land on in "The Wizard of Oz"?

What Halle Berry movie is named for the password in the Marx Brothers" "Horse Feathers"?

The Three Mile Island accident occurred in which US state?

What US Midwestern city garnered the nickname Porkopolis in 19th century?

What US state has been governed by Gifford Pinchot and Milton Shapp?